Cancer glossary

Plain, accurate definitions of the medical terms used on this site.

A

Ablation: Treatments that destroy a small tumour where it is, using heat, cold or another form of energy, usually without the need for a large surgical cut. It is a useful option for people for whom surgery is not suitable.
Active surveillance: Regular monitoring of low-risk cancers (such as some prostate or thyroid cancers) with tests, scans and biopsies instead of treating straight away; treatment is started only if the cancer grows.
Acute lymphoblastic leukaemia (ALL): A cancer in which immature lymphocytes (blasts) quickly multiply in the bone marrow and blood and take the place of healthy cells. It is more common in children, but it also affects adults. Read more
Acute myeloid leukaemia (AML): A fast-growing cancer of the blood and bone marrow in which immature myeloid cells (blasts) multiply and take the place of healthy blood cells. It usually needs treatment straight away. Read more
Acute promyelocytic leukaemia (APL): A type of acute myeloid leukaemia in which immature cells called promyelocytes multiply. There is a high risk of clotting problems and severe bleeding early in the disease. When its specific treatment is started quickly, the chance of a cure is very high. Read more
Adenocarcinoma: A type of carcinoma that starts in gland cells (cells that make and release fluids); common in the lung, stomach, bowel, pancreas and prostate.
Adjuvant therapy: Treatment (such as chemotherapy, radiotherapy, hormone therapy or immunotherapy) given after the main treatment, usually surgery, to lower the chance of the cancer coming back.
Adrenal glands: Two small glands, one on top of each kidney, that make hormones such as cortisol, adrenaline and some sex hormones. These hormones help control stress, blood pressure and blood sugar.
Allogeneic transplant: A transplant of stem cells from a matched donor (a relative or an unrelated person). The donor’s immune cells can also attack the cancer cells. Read more
Alpha-fetoprotein: A protein in the blood that is raised in some liver cancers (hepatocellular carcinoma) and in germ cell tumours. Together with ultrasound, it is used to check the liver of people at high risk. Read more
American Society of Clinical Oncology: The American Society of Clinical Oncology: a professional organisation of cancer specialists that reviews research and publishes evidence-based treatment guidelines for doctors.
Anaemia: A low level of red blood cells or haemoglobin in the blood, which causes tiredness, paleness and shortness of breath. It may be caused by the cancer itself or by its treatment.
Anaphylaxis: A sudden and severe allergic reaction that can cause swelling of the throat, difficulty breathing, a drop in blood pressure and reduced consciousness. It is a medical emergency and needs treatment straight away, usually with adrenaline.
Anaplastic lymphoma kinase: A gene whose rearrangement (fusion) occurs in a small percentage of lung cancers, often in people who have never smoked. There are targeted medicines that block ALK. Read more
Androgen deprivation therapy (ADT): Hormone therapy for prostate cancer that uses medicines or surgery to greatly lower the level of male hormones (androgens such as testosterone). Read more
Androgen receptor pathway inhibitor: Medicines taken by mouth (such as abiraterone, enzalutamide, apalutamide and darolutamide) that block the androgen receptor pathway in prostate cancer more strongly than standard hormone therapy. Read more
Angiogenesis: The process of forming new blood vessels. Tumours make new vessels to grow and to get oxygen and nutrients, and anti-angiogenic medicines try to block this process.
Antibody: A protein the body makes to recognise and attach to foreign invaders such as germs. In cancer treatment, antibodies made in the laboratory stick to a specific target on cancer cells.
Antibody-drug conjugate (ADC): A medicine made of an antibody that sticks to a specific target on cancer cells, joined to a strong chemotherapy drug. It carries the drug straight to the cancer cell. Read more
Anticoagulant: A medicine that slows blood clotting to stop a clot from forming or growing. It is used to prevent and treat blood clots. Its main risk is bleeding, so it must be taken under a doctor’s care.
Antigen: Any substance (often a protein) that the immune system recognises and can mount an immune response against.
Apheresis: A procedure in which blood is taken from the body by a special machine, the part that is needed, such as stem cells, is separated out, and the rest of the blood is returned to the body. It is used to collect cells before a transplant. Read more
Apoptosis: Programmed cell death; a natural process that quietly removes old or damaged cells. Cancer cells often escape it, and many cancer treatments try to switch it back on.
Aromatase inhibitor: A medicine taken by mouth that blocks the aromatase enzyme and lowers the amount of oestrogen made in the body. It is used in hormone-sensitive breast cancer, especially in women after the menopause, to stop the tumour growing or coming back. Read more
Autologous transplant: A transplant of stem cells that were collected from the patient earlier and stored, then given back after high-dose chemotherapy. Read more

B

B cell (B lymphocyte): A type of white blood cell (lymphocyte) that makes antibodies after recognising germs. Many lymphomas and chronic lymphocytic leukaemia arise from cancerous B cells.
B-cell maturation antigen: A protein on the surface of plasma cells and myeloma cells that is a good target for immunotherapy. Treatments such as CAR-T and bispecific antibodies recognise it to target myeloma cells. Read more
Bacillus Calmette–Guérin (intravesical BCG): A weakened bacterium (the same one used in the tuberculosis vaccine) that is put into the bladder as a liquid through a catheter. This immunotherapy activates the immune system and lowers the risk of non-invasive bladder cancer coming back or getting worse. Read more
Benign: A lump or tumour that is not cancer: it does not invade nearby tissues or spread to other parts of the body, although it sometimes needs treatment because of its size or position.
Bilirubin: A yellow pigment made when red blood cells break down, which the liver removes. A high level in a blood test can be a sign of a problem with the liver or bile ducts, and can make the skin and eyes turn yellow (jaundice).
Biochemical recurrence: A new rise in PSA after surgery or radiotherapy for prostate cancer, without the disease being seen on examination or scans. It is a sign that the cancer may be coming back and needs to be checked. Read more
Biomarker: A feature that can be measured in the blood, tissue or other body fluids (such as a gene change or a protein) and shows whether a disease is present, how it is likely to behave, or how likely it is to respond to a particular treatment.
Biopsy: Taking a small piece of tissue or some cells (with a needle, an endoscope or surgery) to look at under a microscope. It is the only certain way to diagnose most cancers.
Bispecific antibody: An antibody that sticks to two different targets at the same time; for example, one end to a cancer cell and the other end to a T cell, to bring the immune cell close to the tumour.
Bisphosphonate: A group of medicines that slow down bone loss. In people with cancer they are used to strengthen the bones, lower the risk of fractures, and treat cancer that has spread to the bone or a high blood calcium level.
Blast cell: An immature blood-forming cell in the bone marrow. Normally there are very few, and a high percentage of them in the blood or bone marrow can be a sign of acute leukaemia. Read more
Blood cancers (haematological malignancies): A group of cancers that start in blood-forming cells or immune cells in the bone marrow and lymphatic system, such as leukaemia, lymphoma and multiple myeloma. In everyday speech, “blood cancer” is often used to mean leukaemia. Read more
Bone marrow: The soft, spongy tissue inside the bones that makes red blood cells, white blood cells and platelets.
Bone mineral density: The amount of minerals (especially calcium) in the bones, which shows how strong they are. It is measured with a simple, low-radiation scan. A fall in bone density, for example after some hormone treatments, raises the risk of fractures.
Boxed warning: The most serious safety warning on a medicine’s official label. It describes possibly severe or life-threatening side effects and is shown in a highlighted box at the start of the drug information.
Brachytherapy: Internal radiotherapy in which a radioactive source is placed inside or close to the tumour; for example, in cervical or prostate cancer.
BRAF gene: A gene whose mutation (especially V600E) is found in some melanomas and in some thyroid, bowel and lung cancers, and can be treated with BRAF and MEK inhibitors.
BRCA1/BRCA2 mutation: An inherited or acquired change in the BRCA1 or BRCA2 genes, which help repair DNA. An inherited mutation in these genes raises the risk of breast, ovarian, prostate and pancreatic cancer.
Breast-conserving surgery: Surgery to remove the tumour together with a margin of healthy tissue while keeping the rest of the breast. It is usually followed by radiotherapy. Read more
BTK inhibitor: Medicines taken by mouth (such as ibrutinib, acalabrutinib and zanubrutinib) that block the signals cancerous B lymphocytes need to survive. They are used in chronic lymphocytic leukaemia and some lymphomas.

C

Cancer antigen 125: A tumour marker in the blood that is raised in many ovarian cancers and is used to follow treatment. It can also be raised in non-cancerous conditions, so it is not recommended for screening. Read more
Carbohydrate antigen 19-9: A tumour marker in the blood that is mainly used in pancreatic cancer and bile duct cancer to follow how well treatment is working. It also rises when the bile ducts are blocked or inflamed. Read more
Carcinoembryonic antigen: A protein that some tumours, especially bowel cancer, release into the blood. It is used to follow treatment and to detect a return of the cancer, but it can also be raised in smokers and in some non-cancerous conditions. Read more
Carcinoma: Cancer that starts in the cells that line the surfaces of organs and glands (epithelial cells). It is the most common type of cancer, and includes most breast, lung, bowel and prostate cancers.
Carcinoma in situ: Cancer cells that have stayed in the layer where they first formed and have not invaded deeper tissues. One example is ductal carcinoma in situ (DCIS) of the breast. Read more
Cardiotoxicity: Damage to the heart caused by some cancer medicines or radiotherapy. It may weaken the heart’s pumping and lead to heart failure, heart rhythm problems or inflammation of the heart. Regular heart checks help.
Castration-resistant prostate cancer: Prostate cancer that keeps growing even though hormone therapy has lowered testosterone to a very low level. Read more
Catheter: A thin, flexible tube put into a vein or an organ to give medicines, take blood samples or drain fluid. It sometimes stays in place for a long time.
CD20: A protein on the surface of B lymphocytes that is found in many B-cell lymphomas and leukaemias. Anti-CD20 antibodies, such as rituximab, attach to it and destroy the cancerous B cells. Read more
CD38: A protein on the surface of plasma cells and some immune cells that is present in large amounts on myeloma cells. Anti-CD38 antibodies, such as daratumumab, stick to it and help destroy myeloma cells. Read more
CDK4/6 inhibitor: Medicines taken by mouth (such as ribociclib, palbociclib and abemaciclib) that stop the cell division cycle. They are used together with hormone therapy in hormone receptor positive breast cancer. Read more
Cell therapy: Treatment in which living cells (often modified immune cells such as CAR-T cells) are given to the patient by infusion to fight the cancer.
Cervix: The narrow lower part of the womb, which opens as a channel into the vagina. Cervical cancer is almost always linked to long-lasting infection with HPV, and screening tests can find it earlier. Read more
Chemoradiotherapy: Chemotherapy and radiotherapy given at the same time; the chemotherapy makes the cancer cells more sensitive to the radiation.
Chemotherapy: Treatment with medicines that kill fast-dividing cells, including cancer cells. It may also harm healthy cells that divide quickly (in the hair, the lining of the mouth and gut, and the bone marrow).
Chimeric antigen receptor T-cell therapy: A type of cell therapy in which the patient’s own T cells are genetically changed in the laboratory so that they can recognise cancer cells, and are then given back to the patient.
Chromosome: Thread-like structures in the nucleus of the cell that carry the DNA and genes. Humans have 23 pairs of chromosomes, and changes in them can play a part in causing some cancers and in their type.
Chronic lymphocytic leukaemia (CLL): A slow-growing blood cancer in which abnormal B lymphocytes gradually build up in the blood, bone marrow and lymph nodes. It is seen mostly in older people, and not every patient needs treatment straight away. Read more
Chronic myeloid leukaemia (CML): A blood cancer in which myeloid cells slowly multiply. It is usually linked to the Philadelphia chromosome and the BCR::ABL1 gene. Targeted medicines taken by mouth control it well in most patients. Read more
Circulating tumour DNA: Small pieces of DNA that enter the blood from cancer cells. Measuring them can show the tumour’s gene changes, disease left behind after treatment, or an early return of the cancer. Read more
Cirrhosis: Widespread, long-term scarring and hardening of the liver (from causes such as hepatitis B or C, alcohol or fatty liver), which greatly raises the risk of liver cancer. Read more
Clinical trial: A research study in human volunteers that tests the safety and effectiveness of a new treatment, test or procedure. All of today’s standard treatments were first tested in trials.
Cohort study: An observational study that follows a group of people over time to see who develops a disease or a particular outcome, and how this is linked to factors such as smoking or treatment.
Colitis: Inflammation of the wall of the large bowel, which causes diarrhoea, tummy pain and sometimes blood or mucus in the stool. In cancer treatment it may be a side effect of immunotherapy and needs prompt treatment. Read more
Colon: The main, long part of the large bowel, which absorbs water and salt from digested food and forms stool. Colon cancer is one of the most common cancers of the digestive system. Read more
Colonoscopy: A look inside the large bowel with a flexible tube that has a camera. The doctor can remove polyps or take samples at the same time. Read more
Colorectal: Relating to the large bowel (colon) and the rectum, the last part of the digestive tract. Colorectal cancer starts in these areas and often develops from polyps. Read more
Combined positive score (PD-L1): A number that shows how many cancer cells and immune cells in a tumour sample carry the PD-L1 protein, compared with the number of cancer cells. It is used to decide about immunotherapy in some cancers.
Complete blood count (CBC): A simple blood test that counts red cells, white cells and platelets and measures haemoglobin. It is widely used for diagnosis and for checking the side effects of cancer treatment. Read more
Complete remission: A state in which the signs and symptoms of cancer have gone after treatment. It is a term often used in blood cancers; remission may last, or the disease may come back later.
Complete response: The disappearance of all measurable signs of cancer on tests and scans after treatment. It does not mean the cancer is definitely cured, because a very small number of cells may still be left.
Conditioning regimen: Treatment with chemotherapy, sometimes with radiotherapy, given before a stem cell transplant to destroy the disease, prepare the bone marrow and stop the body from rejecting the transplant. Read more
Confidence interval (CI): A range of numbers within which the true value of a result (such as a hazard ratio) lies with a stated probability (usually 95%). The narrower it is, the more precise the result.
Consolidation therapy: A stage of treatment after the disease has gone into remission or is first under control, given to destroy any remaining cancer cells and lower the risk of it coming back.
Corticosteroid: Medicines similar to cortisol (a hormone made by the adrenal glands) that reduce inflammation and the immune response, such as dexamethasone and prednisolone. In cancer care they are used to prevent sickness and allergic reactions, to treat some side effects, and also to treat some blood cancers.
Creatinine: A waste product from muscle activity that the kidneys remove from the blood. A high level in a blood test can be a sign that the kidneys are not working as well, and it is checked to adjust the doses of medicines.
Creatinine clearance (CrCl): An estimate of how well the kidneys clean the blood, worked out from the blood creatinine level, age, weight and sex. It is used to adjust the doses of many medicines, including cancer medicines and anticoagulants.
CT scan: A scan that uses X-rays and a computer to make detailed cross-section pictures of the inside of the body. It is used to diagnose, stage and follow up cancer.
Cystectomy: An operation to remove the bladder, either completely or in part, done mostly for bladder cancer that has grown into the muscle. After the whole bladder is removed, a new way for urine to leave the body is made. Read more
Cystoscopy: A look inside the bladder and the urethra with a thin tube that has a camera. It is the main way to diagnose and follow up bladder cancer. Read more
Cytochrome P450 3A4 enzyme: An enzyme, mainly in the liver, that breaks down many medicines. Medicines or foods (such as grapefruit) that block or boost it can change the blood level of some cancer medicines.
Cytogenetics: The study of chromosomes and large genetic changes in cells, under a microscope and with methods such as FISH. In blood cancers it helps with an accurate diagnosis, predicting how the disease will behave and choosing treatment.
Cytokine: Small messenger molecules made by immune cells and other cells to control each other’s activity. With some immunotherapies, the release of large amounts of them can cause fever and low blood pressure.
Cytokine release syndrome (CRS): An inflammatory reaction caused by the release of large amounts of immune messenger substances after treatments such as CAR-T or bispecific antibodies. It causes fever, low blood pressure and shortness of breath, and needs urgent care.
Cytomegalovirus (CMV): A virus of the herpes family that stays silent, without symptoms, in many people. In people with a weak immune system, such as after a bone marrow transplant, it can become active and damage the lungs, bowel or eyes.
Cytotoxic T-lymphocyte–associated protein 4: A protein on T cells that holds back the immune response, like a brake. Medicines that block it release this brake so that the immune system attacks the cancer more strongly, but they may cause immune side effects.

D

Deoxyribonucleic acid: The molecule in every cell that carries genetic information, with the instructions for making proteins and for how the cell works. Damage or mutations in it can lead to cancer.
Diffuse large B-cell lymphoma (DLBCL): The most common type of non-Hodgkin lymphoma. It starts in B lymphocytes (white blood cells that make antibodies) and usually grows quickly, but it often responds well to chemotherapy and immunotherapy. Read more
Direct oral anticoagulant: A group of blood-thinning tablets that directly block one of the clotting factors. They are used to prevent and treat blood clots. Read more
Disease progression: The tumour getting bigger, new areas of cancer appearing, or the cancer spreading, during or after treatment.
Disease-free survival (DFS): The length of time after treatment meant to cure the cancer (such as surgery) that a patient lives with no sign of the cancer coming back.
Double-blind: A trial design in which neither the patients nor the researchers know which treatment each person is getting, so that expectations do not affect the results.
DPD deficiency (DPYD): A lack or low activity of an enzyme the body needs to break down fluorouracil and capecitabine. In this case the medicine builds up and causes severe side effects; a gene test before treatment can find it. Read more
Dysplasia: An abnormal change in the shape and arrangement of the cells of a tissue that is not yet cancer. Its severity varies, and in more severe cases it may turn into cancer, so it needs follow-up.

E

Endocrine glands: Glands such as the thyroid, pituitary, adrenal glands, pancreas and the ovaries or testicles that make hormones and release them straight into the blood. These hormones control growth, metabolism and the body’s balance.
Endoscopic ultrasound (EUS): A procedure in which a thin endoscope with an ultrasound probe is passed through the mouth into the oesophagus, stomach or bowel. It gives a close, detailed picture of the wall of the digestive tract and nearby organs such as the pancreas, and samples can be taken if needed.
Endoscopy: A look inside the body (such as the oesophagus, stomach or bowel) with a thin, flexible tube that has a camera and a light. It also allows samples to be taken.
Endpoint (trial outcome): The measure chosen in a clinical trial to judge the effect of a treatment, such as overall survival, progression-free survival, tumour response or quality of life. The result of the study is judged on this measure. Read more
Engraftment: The stage after a stem cell transplant when the transplanted cells settle in the bone marrow and start making healthy white cells, platelets and red cells again. Read more
Epidermal growth factor receptor: A receptor on the cell surface that drives growth. Mutations in it are found in some non-small cell lung cancers and are treated with targeted medicines taken by mouth. Read more
Epstein–Barr virus (EBV): A common virus of the herpes family that causes glandular fever (mononucleosis) and causes no symptoms in most people. In some people, especially those with a weak immune system, it is linked to certain lymphomas and other cancers.
Erythropoietin / erythropoiesis-stimulating agents (ESA): A hormone made by the kidneys that drives the bone marrow to make red blood cells. Its medicine form is sometimes used for anaemia caused by chemotherapy, but it can raise the risk of blood clots.
ESR1 gene (oestrogen receptor): The gene that holds the instructions for making the oestrogen receptor. Mutations in it usually appear after hormone therapy (especially with aromatase inhibitors) in advanced breast cancer. They cause resistance to some medicines and matter when choosing the next treatment. Read more
European Medicines Agency: The European agency that assesses medicines for quality, safety and effectiveness and recommends whether they should be approved for use in the European Union.
European Society for Medical Oncology: The European Society for Medical Oncology: a scientific organisation of cancer specialists that publishes evidence-based guidelines for diagnosing and treating cancers.
Event-free survival (EFS): The length of time a patient lives without a pre-defined “event” happening (such as the disease getting worse, the cancer coming back, not being able to have the planned surgery, or death). It is usually used in trials of treatment given before and after surgery.
External beam radiotherapy: Radiotherapy from a machine outside the body that aims the radiation precisely at the tumour. It is painless, and the patient does not become radioactive after a session, so it is safe to be around other people.
Extravasation: Leakage of a medicine from the vein into the surrounding tissues during an intravenous injection. Some chemotherapy medicines can then cause pain, redness, swelling and tissue damage; tell the nurse straight away.

F

Faecal immunochemical test: A simple stool test for hidden blood, with the sample collected at home. It is used to screen for bowel cancer (usually once a year). A positive result should be followed up with a colonoscopy. Read more
Febrile neutropenia: A fever in a person whose blood has very few neutrophils (white blood cells that fight infection), often after chemotherapy. It is a medical emergency and needs urgent assessment and treatment with antibiotics. Read more
Fertility preservation: Methods used before cancer treatment to keep the ability to have children in the future, such as freezing eggs, embryos or sperm, or operations that keep the womb and ovaries. Read more
FIGO staging: The international system for staging cancers of the female reproductive organs (such as the ovaries, womb and cervix). It shows how far the disease has spread, from stage 1 to 4, and helps choose treatment. It is named after the International Federation of Gynaecology and Obstetrics.
Fine-needle aspiration (FNA): A biopsy with a very thin needle that draws out a few cells or a small amount of fluid from a lump or gland to be looked at under a microscope. It is quick, causes little pain and usually does not need an anaesthetic.
First-line therapy: The first treatment given for a disease (for example, advanced cancer). If the disease gets worse, the next treatments are called second-line, third-line and so on.
Five-year survival: The percentage of patients who are alive 5 years after diagnosis or the start of treatment. This number is an average for a group and cannot predict what will happen to any one person.
Flow cytometry: A test that identifies and counts cells from the blood, bone marrow or tissue by the markers on their surface. It plays an important role in diagnosing leukaemia and lymphoma and working out their type.
FLT3 gene: A gene involved in the growth of blood-forming cells. Its mutations (such as FLT3-ITD) are found in some patients with acute myeloid leukaemia, affect the outlook, and have specific targeted medicines. Read more

G

Gastrointestinal stromal tumour: A rare type of sarcoma that starts in the wall of the digestive tract, most often the stomach or small bowel. It often has a KIT or PDGFRA mutation. The main treatment is surgery, and in high-risk or advanced cases a targeted medicine (such as imatinib) is used.
Gene rearrangement: A change in DNA in which part of a gene moves to another place or joins with another gene. This can make an abnormal protein that is always switched on and drives the growth of cancer cells, and it can sometimes be treated with targeted medicines.
Genetic counselling: A talk with a genetics specialist to assess the risk of inherited cancer based on family history, decide about genetic testing, and explain what the results mean for the person and their family.
Genetic testing: Checking the DNA in a sample of blood, saliva or tissue to look for gene changes. It can show inherited mutations or mutations in the tumour itself, and can help choose treatment. Read more
Germline: Refers to genetic changes inherited from the parents that are present in every cell of the body and can be passed on to children.
Gleason score: A score the pathologist gives based on the pattern of prostate cancer cells under a microscope. It shows how different the tumour is from healthy tissue and how aggressive it is. A higher score means a higher-risk tumour; today it is summed up as the “ISUP grade group”. Read more
Glioblastoma: The most aggressive type of glioma (grade 4) and the most common malignant tumour that starts in the brain in adults. Read more
Glioma: Tumours that start in the supporting cells of the brain and spinal cord (glial cells). They range from slow-growing to very aggressive. Read more
GnRH (LHRH) agonist: An injected medicine that, when used continuously and after a short rise at first, greatly lowers the making of sex hormones (testosterone or oestrogen) in the testicles or ovaries. It is used in prostate cancer and in some hormone-dependent breast cancers.
Graft-versus-host disease (GVHD): A complication after a stem cell transplant from a donor (allogeneic transplant) in which the donor’s immune cells attack the patient’s own tissues, such as the skin, bowel and liver. It can be mild or serious. Read more
Granulocyte colony-stimulating factor: A natural protein that drives the bone marrow to make neutrophils (white blood cells that fight infection). Its medicine form, such as filgrastim, is injected after chemotherapy to lower the risk of infection, and also to collect stem cells. Read more
Gray (Gy), unit of radiation dose: The unit used to measure the dose of radiation absorbed by the body’s tissues. The amount of radiotherapy is set in grays and in the number of sessions. Read more

H

Haematopoietic stem cell transplantation: Replacing damaged bone marrow with healthy blood-forming stem cells, usually after high-dose chemotherapy. It is used in blood cancers such as myeloma, leukaemia and lymphoma. Read more
Haemoglobin: An iron-containing protein inside red blood cells that carries oxygen from the lungs to the body’s tissues. A low level is a sign of anaemia and can cause tiredness, paleness and shortness of breath.
Haploidentical (half-matched) donor: A transplant in which the donor, such as a parent, child, brother or sister, shares only half of the HLA markers with the patient. With today’s methods, it is an accepted option when no fully matched donor is available. Read more
Hazard ratio (HR): A number that compares the risk of an event (such as the disease getting worse, or death) between two groups. An HR of 0.70 means the risk in the new treatment group was about 30% lower at any point in time; an HR of 1 means there is no difference.
Helicobacter pylori: A bacterium that lives in the stomach. Long-term infection with it is the most important risk factor for stomach cancer, and treating the infection can lower the risk. Read more
Hepatitis B: A viral infection of the liver that, if it becomes long-term, can lead to cirrhosis and liver cancer. It can be prevented with a vaccine. Read more
Hepatocellular carcinoma (HCC): The most common type of cancer that starts in the liver. It begins in the main liver cells (hepatocytes) and usually develops in people with cirrhosis or long-term hepatitis. Read more
HER2-low: A group of breast cancers that have a small amount of HER2 (an immunohistochemistry score of 1+ or 2+ without extra copies of the gene). Some antibody-drug conjugates also work in this group. Read more
Hodgkin lymphoma: A type of lymphoma recognised by special large cells called Reed-Sternberg cells. It is often seen in young people. Most patients are cured with today’s treatment. Read more
Homologous recombination deficiency: The cell’s inability to repair breaks in both strands of DNA accurately. Tumours that have it, for example in ovarian cancer, are usually more sensitive to PARP inhibitors and platinum drugs. Read more
Hormone receptor: Proteins in breast cancer cells that respond to oestrogen or progesterone. “Hormone receptor positive” cancer usually responds to hormone therapy. Read more
Hormone therapy: Treatment that lowers or blocks the making or the effect of hormones such as oestrogen or testosterone, to slow the growth of hormone-dependent cancers (breast, prostate).
Hormone-sensitive: Cancer (such as prostate cancer) whose growth still depends on hormones and that responds to treatments that lower or block hormones. Read more
Human epidermal growth factor receptor 2: A protein on the cell surface that drives growth. It is made in excess (HER2 positive) in about one in five breast cancers and in some stomach cancers, and it is the target of anti-HER2 medicines. Read more
Human leukocyte antigen: A group of proteins on the surface of cells that the immune system uses to tell the body’s own cells from foreign ones. A good match between the patient and the donor is very important in stem cell transplants. Read more
Human papillomavirus: A common virus passed on through sexual contact. Long-lasting infection with its high-risk types causes almost all cervical cancers and some cancers of the throat, anus and genitals. Read more
Hydration (IV fluids): Giving the body enough fluids, usually through a drip into a vein before some medicines or when someone is dehydrated. Its aim is to protect the kidneys and help the body get rid of medicines and waste products.
Hypercalcaemia: A high level of calcium in the blood that happens in some cancers, especially when the bones are involved. It can cause thirst, nausea, constipation, drowsiness and confusion, and needs urgent treatment. Read more
Hypophysitis: Inflammation of the pituitary gland at the base of the brain, which can cause headache, tiredness and hormone problems. It is a rare side effect of immunotherapy and is usually treated by replacing the missing hormones. Read more
Hypothyroidism: A condition in which the thyroid gland does not make enough hormone, which can cause tiredness, feeling the cold, weight gain and a general slowing down. Some cancer treatments cause it, and it is treated with thyroid hormone tablets.

I

IDH1/IDH2 genes: Genes that make enzymes important for the cell’s metabolism. Mutations in them are found in some gliomas and in acute myeloid leukaemia, and they matter for diagnosis and for choosing targeted treatment.
Immune checkpoint inhibitor: Medicines (such as anti-PD-1, anti-PD-L1 or anti-CTLA-4 drugs) that release the “brakes” on the immune system so that T cells can attack cancer cells.
Immune effector cell-associated neurotoxicity syndrome: A nervous system side effect after treatments such as CAR-T or bispecific antibodies. It shows up as confusion, trouble speaking, shaking or seizures, and needs urgent assessment.
Immune system: A network of cells and organs that defends the body against germs and abnormal cells. Immunotherapy helps fight cancer by strengthening this system.
Immune-related adverse events: Side effects caused by the activated immune system attacking healthy tissues after immunotherapy, such as inflammation of the bowel, lungs, liver, skin or glands (for example, an underactive thyroid).
Immunoglobulin (IVIG): Proteins in the blood, the same as antibodies, that fight infection. Their injectable form (IVIG) is made from donated blood and is used when antibodies are lacking and in some immune diseases.
Immunohistochemistry (IHC): A way of staining tissue with special antibodies to show whether proteins such as HER2, hormone receptors or PD-L1 are present on tumour cells.
Immunosuppressive drug: A medicine that lowers the activity of the immune system; for example, after a transplant to prevent rejection and graft-versus-host disease, or in autoimmune diseases. Taking it makes the body more vulnerable to infections.
Immunotherapy: Treatment that helps the body’s immune system to recognise and destroy cancer cells better, such as immune checkpoint inhibitors, CAR-T cell therapy and treatment vaccines.
Induction therapy: The first stage of treatment, especially in leukaemias and multiple myeloma. Its aim is to reduce the disease quickly and reach remission, opening the way for later treatments such as consolidation therapy or a transplant.
Infusion-related reaction: A reaction that happens during a drip of a medicine or shortly after it, and may cause fever, chills, itching, shortness of breath or low blood pressure. If it happens, the infusion is slowed or stopped and the needed treatment is started.
International normalised ratio: A number from a blood test that shows how fast the blood clots. It is used to monitor the medicine warfarin, and a high value raises the risk of bleeding.
Interstitial lung disease (ILD): A group of diseases that inflame or stiffen the tissue between the air sacs of the lungs, causing shortness of breath and a dry cough. Some cancer medicines can cause this problem.
Intravenous infusion: A slow, controlled injection of a medicine or fluid into a vein, usually through a drip, over minutes to hours. Many chemotherapy and immunotherapy medicines are given this way.
Invasive cancer: Cancer that has grown beyond the layer where it started into nearby tissues and is able to spread.
ISUP grade group: A system for grading prostate cancer from 1 to 5 based on how the cells look under a microscope. A higher number means a more aggressive tumour, and it plays an important role in choosing treatment. Read more

K

Kinase: An enzyme that switches other proteins on or off by attaching a phosphate group to them, passing on signals for growth and division within the cell. In some cancers it is overactive, and targeted medicines block it.
KRAS gene: One of the RAS family of genes. Its mutations are among the most common in pancreatic, bowel and lung cancer, and until recently it was very hard to target with medicines.

L

Left ventricular ejection fraction (LVEF): The percentage of the blood in the heart’s left ventricle that is pumped out with each beat. It shows how well the heart is working, and some cancer medicines can lower it.
Leukaemia: Cancer of the blood-forming cells in the bone marrow that causes too many abnormal white blood cells to be made. Its types are acute or chronic, and myeloid or lymphoid. Read more
Liquid biopsy: A blood test (or a test of other body fluids) that looks for pieces of DNA or cancer cells released by a tumour, without the need to take a tissue sample. Read more
Liver enzymes (ALT, AST): Enzymes such as ALT and AST that are found in liver cells. Their level in the blood rises when the liver is damaged, so they are measured to check the effect of medicines on the liver.
Lobectomy: An operation to remove a whole lobe of an organ such as the lung or thyroid. In lung cancer, it is the standard treatment for many early-stage tumours.
Locally advanced: Cancer that has spread from where it started into nearby tissues or lymph nodes, but has not reached distant organs.
Low-dose CT: A type of chest CT scan that uses much less radiation. It is used to screen for lung cancer in people at high risk (current or former smokers who have smoked heavily). Read more
Low-molecular-weight heparin (LMWH): A type of anticoagulant injected under the skin that stops blood from clotting. It is used to prevent and treat clots in the veins in people with cancer, and needs less monitoring than standard heparin. Read more
Lymph nodes: Small bean-shaped structures throughout the body that are part of the immune system. Cancer often spreads first to nearby lymph nodes, so checking them is important for staging.
Lymphocyte: A type of white blood cell, including B cells, T cells and natural killer cells, that takes part in the immune response. They are found in the blood and in lymphatic tissues such as the lymph nodes.
Lymphoma: Cancer of lymphocytes (a type of white blood cell) that usually grows in the lymph nodes, spleen or bone marrow. Its two main groups are Hodgkin and non-Hodgkin lymphoma. Read more
Lynch syndrome: The most common inherited syndrome causing bowel cancer. It is caused by an inherited mutation in DNA repair genes and raises the risk of cancer of the bowel, womb, ovaries and some other organs. Read more

M

Magnetic resonance imaging: A scan that uses a strong magnetic field and radio waves (no X-rays) to make very detailed pictures of soft tissues such as the brain, liver, pelvis and breast.
Maintenance therapy: Treatment that is continued after the disease has responded to the first treatment, to keep it under control for longer and prevent it from coming back or getting worse.
Malignant: Cancerous; a lump that can invade nearby tissues and spread through the blood or lymph to other parts of the body.
Mammography: A low-dose X-ray of the breast used to screen for or diagnose breast cancer. Read more
Mantle cell lymphoma (MCL): A type of non-Hodgkin lymphoma that starts in B lymphocytes of the “mantle” zone of the lymph nodes. It usually causes enlarged lymph nodes and can also affect the bone marrow and the digestive tract. Read more
Mastectomy: Surgery to remove the whole breast, to treat or prevent breast cancer. Read more
Median: The middle number when the data are put in order. For example, a median survival of 20 months means half of the patients lived less than 20 months and half lived longer; many patients live much longer than the median.
Melanoma: Cancer of the pigment-making cells of the skin (melanocytes). It is less common than other skin cancers, but if it is found late it is more likely to spread. Read more
Messenger RNA: RNA is a molecule similar to DNA that helps make proteins; mRNA (messenger RNA) is a copy of a gene that carries the instructions for making a protein from the DNA to the protein-making part of the cell. Read more
Meta-analysis: A statistical method that combines the results of several similar studies to reach a more precise and reliable conclusion.
Metastasis: The spread of cancer cells from the place where the tumour first started to other parts of the body (such as the liver, lungs, bones or brain) through the blood or lymph. Cancer that has spread in this way is called “metastatic” or stage 4.
MGMT gene (promoter methylation): A gene that makes an enzyme to repair DNA damage. When it is switched off by methylation in glioblastoma, the tumour is likely to respond better to chemotherapy such as temozolomide. Read more
Microsatellite instability / mismatch repair deficiency: A state in which the system that repairs DNA errors in the tumour cell is faulty, so many mutations build up. These tumours often respond very well to immunotherapy. Read more
Minimal (measurable) residual disease (MRD): A very small number of cancer cells left in the body after treatment that cannot be seen with routine tests but can be found with very sensitive methods. “MRD negative” means no such cells were found.
Monoclonal antibody: A protein made in the laboratory that, like a natural antibody, sticks to one particular target (for example HER2 or CD20). The names of most of these medicines end in “-mab”.
Monoclonal gammopathy of undetermined significance: A small amount of a monoclonal protein in the blood, without symptoms or damage to the organs. It is not cancer, but each year a small percentage of people go on to develop myeloma or a similar disease, so regular check-ups are needed. Read more
Mucositis: Inflammation and sores of the inner lining of the mouth and digestive tract. It is a common side effect of chemotherapy and of radiotherapy to the head and neck, and can make eating and drinking painful.
Multiple myeloma: Cancer of plasma cells (the cells that make antibodies) in the bone marrow. It can damage the bones, the kidneys and the making of blood cells, and it produces an abnormal protein called M protein. Read more
Mutation: A change in the DNA sequence of a gene. Mutations can be inherited or can arise during life in tumour cells, and some of them are targets for specific medicines.
Myelodysplastic syndrome (MDS): A group of bone marrow diseases in which the blood-forming cells do not mature properly and the number of healthy blood cells falls. In some patients it may turn into acute myeloid leukaemia. Read more
Myocarditis: Inflammation of the heart muscle, which can cause chest pain, a racing or pounding heart, shortness of breath or heart failure. It is a rare side effect of immunotherapy or some cancer medicines and must be checked straight away. Read more

N

National Comprehensive Cancer Network: An alliance of cancer centres in the United States that publishes up-to-date clinical guidelines for diagnosing and treating many types of cancer.
Neoadjuvant therapy: Treatment given before surgery to shrink the tumour, make the operation easier or smaller, and see how well the tumour responds to the medicine.
Neoantigen: New proteins made only in cancer cells because of their mutations, which the immune system can recognise as foreign. They are the basis of personalised cancer vaccines. Read more
Neutropenia: A low level of neutrophils (a type of white blood cell that fights infection), which often happens after chemotherapy. A fever at this time (“febrile neutropenia”) is a medical emergency.
Neutrophil: A type of white blood cell that is the body’s first line of defence against bacterial and fungal infections. Having too few after chemotherapy raises the risk of serious infections. Read more
Next-generation sequencing (NGS): A technology that can check tens to hundreds of genes at the same time in a tumour or blood sample, to find gene changes that can be targeted by treatment.
Nodule: A small, round lump or spot in an organ, such as the lung or thyroid, often seen on a scan. Most nodules are benign, but some need follow-up or a biopsy.
Non-Hodgkin lymphoma: A large group of lymphomas (without Reed-Sternberg cells) that start in B or T lymphocytes. They can be slow-growing or aggressive. Read more
Non-inferiority: A trial design that aims to show that a new treatment is not worse than the standard treatment by more than a small, pre-set amount. It is usually used when the new treatment has fewer side effects or is more convenient. Read more
Non-small cell lung cancer (NSCLC): The most common group of lung cancers. It starts in lung cells and grows more slowly than the small cell type. Its main types are adenocarcinoma, squamous cell and large cell carcinoma. Read more
NPM1 gene: A gene involved in basic cell functions. Its mutation is found in about one third of acute myeloid leukaemias. When there are no other high-risk mutations, it usually goes with a better outlook, and it is also used to monitor disease left behind after treatment. Read more

O

Objective response rate (ORR): The percentage of patients whose tumour has shrunk by a set amount after treatment (partial response) or has disappeared completely (complete response).
Oncologist: A doctor who specialises in diagnosing and treating cancer. A medical oncologist gives drug treatment, a radiation oncologist gives radiotherapy and a surgical oncologist operates on cancer.
Organ preservation: Treatment approaches that aim to control the cancer without removing the affected organ (such as the rectum, bladder or voice box), so that the organ keeps working and quality of life is protected. Read more
Overall survival (OS): The length of time patients live from the start of treatment or from diagnosis, whatever the cause of death. It is the most important and most reliable measure of whether a treatment helps in clinical trials.

P

Palliative care: Care that focuses on easing pain and other symptoms and improving the quality of life of the patient and family. It can be given at any stage of the illness, alongside cancer treatment.
Pancreas: An organ behind the stomach that makes digestive enzymes and hormones such as insulin. It helps digest food and control blood sugar. Read more
Pap test: Taking a sample of cells from the cervix and looking at it under a microscope to find precancerous or cancerous changes. Read more
PARP inhibitor: Medicines taken by mouth (such as olaparib) that block one of the DNA repair pathways. They work especially well in tumours with a BRCA mutation or a defect in DNA repair.
Pathological complete response (pCR): No invasive cancer cells found by the pathologist in the tissue removed at surgery after treatment given before the operation. It usually goes with a better outlook.
Pathology: The study of tissue or cells under a microscope by a pathologist to find out the type, grade and features of a cancer. The pathology report is the basis for treatment decisions.
Performance status (ECOG): A measure of how well a patient can carry out daily activities, usually given on the ECOG scale from 0 (fully active) to 4 (completely bed-bound). Doctors use it to judge how well a patient can cope with treatments such as chemotherapy.
Perioperative therapy: Treatment given both before and after surgery; that is, a combination of treatment before surgery and adjuvant (follow-up) treatment.
Peripheral neuropathy: Damage to the nerves outside the brain and spinal cord, which causes numbness, tingling, burning or pain in the hands and feet. It is a side effect of some chemotherapy drugs such as oxaliplatin and the taxanes.
PET scan / PET-CT: A scan done after injecting a small amount of a radioactive substance (such as labelled sugar) that makes very active tissues, such as tumours, light up. It is usually done together with a CT scan.
Phase 1 trial: The first stage of testing a new medicine in people, usually with a small number of patients, to find the right dose and check its safety.
Phase 2 trial: A stage of a trial that checks whether a medicine works against a particular type of cancer and looks more closely at its side effects.
Phase 3 trial: A large trial, usually randomised, that compares a new treatment with the standard treatment. Its results are often the basis for approving a medicine and for changing treatment guidelines.
Philadelphia chromosome: An acquired genetic change caused by pieces swapping places between chromosomes 9 and 22, which creates the BCR::ABL1 gene. It is found in chronic myeloid leukaemia and in some acute lymphoblastic leukaemias. Read more
Pituitary gland: A gland the size of a pea at the base of the brain. By releasing hormones it controls other glands, such as the thyroid, adrenal glands and sex glands, as well as the body’s growth. It is also called the “master gland”.
Placebo: A dummy substance or treatment that looks like the real medicine and is given to the control group in trials for comparison. In cancer, a placebo is usually given together with standard treatment, not instead of it.
Plasma cell: A type of white blood cell, grown from a B lymphocyte, that makes antibodies. Cancer of these cells is called multiple myeloma. Read more
Platelet: Very small particles in the blood that stop bleeding by forming clots. Having too few of them, for example after chemotherapy, raises the risk of bruising and bleeding. Read more
Platinum-based chemotherapy: Chemotherapy with medicines that contain platinum, such as cisplatin, carboplatin and oxaliplatin, which damage the DNA of cancer cells.
Platinum-resistant: Cancer (especially ovarian cancer) that comes back or gets worse within a short time (usually less than 6 months) after platinum-based chemotherapy has finished. Read more
Pneumonitis: Inflammation of the lung tissue, which can happen without an infection and causes a dry cough, shortness of breath and fever. It is sometimes a side effect of certain cancer medicines or of radiotherapy. Read more
Polyp: A small growth of tissue that grows from the inner wall of the bowel or other organs. Most polyps are benign, but some (adenomas) can turn into cancer, so they are removed during colonoscopy. Read more
Precancerous: Abnormal changes in cells that are not yet cancer but may turn into cancer over time, such as some bowel polyps or changes in the cervix. Treating them prevents cancer.
Premedication: Medicines given before the main treatment (such as chemotherapy or an antibody infusion) to lower the risk of allergic reactions, nausea or other side effects.
Primary tumour: The tumour in the organ where the cancer first started. Even if the cancer spreads to another organ, it is still named after the primary tumour; for example, breast cancer that has spread to the bones is still breast cancer.
Prognosis: An estimate of how the disease is likely to develop and the chance of recovery or survival, based on the type and stage of the cancer, the features of the tumour and the patient’s general health.
Programmed cell death protein 1: A protein on T cells that acts like a brake. Anti-PD-1 medicines (such as pembrolizumab and nivolumab) release this brake.
Programmed death-ligand 1: A protein that some cancer cells make to switch off T cells. The amount of it in tumour tissue is sometimes measured to help predict whether immunotherapy will help.
Progression-free survival (PFS): The length of time during and after treatment that a patient lives without the disease getting worse (progressing). It is a common way to measure how well a treatment works in clinical trials.
Prophylaxis: Using a medicine or another preventive step before a problem appears, to lower the chance of a disease or complication such as infection, a blood clot or nausea, especially in people at higher risk.
Prostate-specific antigen: A protein made by the prostate gland and measured in the blood. A high level can be caused by cancer, by a non-cancerous enlarged prostate or by inflammation of the prostate. It is used for screening and for follow-up of prostate cancer. Read more
Prostate-specific membrane antigen: A protein found in large amounts on the surface of most prostate cancer cells. It is targeted both in PET scans and in radioligand therapy. Read more
Pulmonary embolism: A blockage of one of the blood vessels in the lungs by a blood clot, which usually comes from the veins in the legs. It can cause sudden shortness of breath, chest pain and cough, and is a medical emergency; people with cancer are at higher risk. Read more

Q

QT interval: A part of the heart tracing (ECG) that shows how long the electrical activity of each beat of the ventricles lasts until they are ready for the next beat. Some medicines lengthen it, which can lead to a dangerous heart rhythm problem.
Quality of life: How satisfied and able a person is in daily life, physically, mentally and socially. In cancer trials it is measured alongside survival.

R

Radioactive iodine therapy: Treatment with radioactive iodine taken by mouth, which is taken up by thyroid cells. It is used after surgery for some thyroid cancers to destroy any remaining thyroid tissue or areas of spread. Read more
Radioligand therapy: A treatment that joins a radioactive substance to a molecule that sticks specifically to cancer cells (such as lutetium-177-PSMA in prostate cancer), so that the radiation goes straight to the tumour. Read more
Radiotherapy: The use of high-energy rays (such as X-rays or protons) to kill cancer cells or shrink a tumour. It is given from outside the body or from a radioactive source placed inside the body.
Randomised controlled trial: A trial in which participants are put by chance (as in a draw) into either the new treatment group or the comparison group. It is the most reliable way to compare treatments.
Rectum: The last part of the large bowel, just before the anus, where stool is stored until it is passed. Cancer of the colon and rectum together is called colorectal cancer or bowel cancer. Read more
Recurrence / relapse: The return of cancer after a period when treatment had removed it or it could not be found. It can come back in the same place (local recurrence) or in other parts of the body.
Red blood cell: Blood cells that carry haemoglobin and take oxygen from the lungs to the body’s tissues. Too few of them leads to anaemia, tiredness and shortness of breath, and a blood transfusion is sometimes needed after chemotherapy.
Refractory: Cancer that does not respond to treatment, or that gets worse during treatment.
Renal cell carcinoma (RCC): The most common kidney cancer. It starts in the cells lining the tiny tubes of the kidney and is often seen as a lump in the kidney. Depending on the stage, it is treated with surgery, monitoring or medicines. Read more
RET gene: A gene that holds the instructions for a protein involved in the growth and development of cells. Its mutation or fusion occurs in some lung and thyroid cancers, and there are specific targeted medicines for it.

S

Sarcoma: Cancer that starts in connective tissues such as bone, cartilage, fat, muscle or blood vessels. It is much rarer than carcinomas.
Screening: Testing people who have no symptoms to find cancer or a precancerous change, so that the disease is found at an early stage when it is easier to treat. Read more
Second-line therapy: Treatment used after the first treatment has not worked, could not be tolerated, or the disease got worse on it. If this treatment does not work either, it is the turn of third-line and later treatments.
Sentinel lymph node: The first lymph node that lymph fluid from a tumour drains into. A biopsy of it shows whether the cancer has reached the lymph nodes, and can sometimes avoid the need to remove many nodes.
Sepsis: A dangerous, body-wide reaction to an infection that can lead to low blood pressure and organ damage. It is more common in people with cancer, especially when their white blood cell count is low, and needs urgent hospital treatment.
Small cell lung cancer (SCLC): A type of lung cancer that grows and spreads quickly and is very closely linked to smoking. It usually responds well to chemotherapy at first, but often comes back soon. Read more
Smouldering multiple myeloma: A stage before active myeloma in which abnormal plasma cells are present but have not yet damaged the organs (bones, kidneys, blood). It is usually watched closely, and in high-risk cases it may be treated. Read more
Solid tumour: An abnormal lump of tissue that forms in an organ (such as the lung, breast or stomach), as opposed to blood cancers such as leukaemia, which do not form a solid lump.
Somatic: Refers to mutations that arise during life only in tumour cells. They are not inherited and are not passed on to children.
Spinal cord compression: Pressure on the spinal cord, often caused by a tumour or by cancer spreading to the spine. It can cause back pain, weakness or numbness in the legs, and problems with passing urine or stool, and is a medical emergency. Read more
Squamous cell carcinoma: A type of carcinoma that starts in the thin, flat cells that line the skin, mouth, throat, oesophagus, lungs or cervix.
Staging: Working out how far a cancer has spread in the body (the size of the tumour, whether lymph nodes are involved and whether it has spread further). The stage is usually given as a number from 0 to 4 and plays a key role in choosing treatment and in the outlook.
Stem cell: Early cells that can copy themselves and turn into specialised cells. Blood-forming stem cells in the bone marrow make red cells, white cells and platelets. Read more
Stent: A very small mesh or hollow tube placed in a narrowed or blocked passage, such as the oesophagus, a blood vessel, the bile duct or the bowel, to keep it open and ease symptoms such as trouble swallowing or jaundice.
Stereotactic radiosurgery / SBRT: A very precise type of radiotherapy that gives a high dose of radiation to a small tumour in one or a few sessions, while largely sparing the healthy tissue around it. Despite its name, it is not surgery.
Supportive care: Care to prevent and manage the problems caused by cancer and its treatment (such as nausea, infection, anaemia, pain and eating problems).
Systemic therapy: Drug treatment that travels through the blood to the whole body and targets cancer cells wherever they are, such as chemotherapy, hormone therapy, targeted therapy and immunotherapy.

T

T cell (T lymphocyte): A type of lymphocyte and a key immune cell that recognises and destroys infected or abnormal cells. Many immunotherapies, such as CAR-T, work by strengthening these cells.
Targeted therapy: Medicines that specifically target molecules or gene changes that the cancer cell depends on to grow. Usually the tumour is tested for the target before the medicine is prescribed.
Thrombocytopenia: A low number of platelets in the blood, which raises the risk of bruising and bleeding. It is a common side effect of chemotherapy and of some blood cancers.
Thyroid-stimulating hormone: A hormone made by the pituitary gland that tells the thyroid to make its hormones. Measuring it in the blood is used to diagnose an underactive or overactive thyroid.
Thyroidectomy: An operation to remove all or part of the thyroid gland. It is used in thyroid cancer, and after the whole gland is removed, thyroid hormone tablets must be taken for life. Read more
TNM staging system: The international system for staging cancer: T describes the size and spread of the primary tumour, N whether lymph nodes are involved, and M whether or not the cancer has spread to distant parts of the body (metastasis).
Total body irradiation (TBI): Radiation given to the whole body before a stem cell transplant. It destroys the diseased cells and the patient’s immune system to make room for the transplanted cells and to stop the transplant from being rejected.
Toxicity: The unwanted effects of a treatment on healthy tissues. Its severity is usually reported as a grade from 1 (mild) to 5 (death).
TP53 gene: A gene that acts like a guard of the cell, stopping damaged cells from multiplying. Its mutations are found in many cancers, and in blood cancers they usually point to a higher-risk disease that is harder to treat.
Transarterial chemoembolisation: A treatment for liver tumours in which a chemotherapy medicine is injected straight into the artery that feeds the tumour, and the vessel is then blocked to cut off the tumour’s blood supply. Read more
Transurethral resection of bladder tumour: Removing a bladder tumour through the urethra with special instruments, without any cut in the skin. It is used both to diagnose the tumour and find out how deep it goes, and to treat bladder cancer that has not grown into the muscle. Read more
Triple-negative breast cancer: A type of breast cancer that has neither oestrogen nor progesterone receptors and does not make too much HER2; so it does not respond to hormone therapy or anti-HER2 medicines. Read more
Tumour: A lump of cells that have grown too much and out of control. It may be benign and not spread anywhere else, or malignant (cancerous) and spread into nearby tissues or distant organs. Read more
Tumour grade: How abnormal the cancer cells look under a microscope. A higher grade usually means the tumour grows faster and is more aggressive. Grade is different from stage (how far the cancer has spread).
Tumour lysis syndrome (TLS): A complication that happens when a large number of cancer cells die quickly, usually at the start of treatment, and spill their contents, such as potassium and uric acid, into the blood. It can damage the kidneys and heart, so it needs prevention and monitoring. Read more
Tumour marker: A substance (often a protein) in the blood that is made by the tumour, or by the body in response to it, such as PSA, CEA or CA-125. It is mostly used to follow treatment and is not enough on its own to diagnose cancer.
Tyrosine kinase inhibitor (TKI): Targeted medicines, usually taken by mouth, that block tyrosine kinase enzymes, which pass growth signals within the cell; for example, medicines against EGFR or BCR-ABL.

U

Ultrasound: A scan that uses sound waves (no radiation) to look at organs such as the liver, thyroid, breast and ovaries. It is also used to guide biopsies.
Umbilical cord blood: Blood taken from the umbilical cord and placenta after birth, which is rich in blood-forming stem cells. It can be stored and used in stem cell transplants to treat blood diseases. Read more
Uric acid: A substance made in the blood from the breakdown of cells and some foods, and removed by the kidneys. It may rise when cancer cells die quickly, and can damage the kidneys.
US Food and Drug Administration: The United States Food and Drug Administration, which reviews and approves medicines and medical products for effectiveness and safety and publishes the official drug label information.
US Preventive Services Task Force: An independent panel of experts in the United States that reviews the scientific evidence and publishes official recommendations on screening for and preventing diseases, including several cancers. Read more

V

Vascular endothelial growth factor: A protein that drives the growth of new blood vessels. Tumours use it to feed themselves, and anti-VEGF medicines (such as bevacizumab) block this process.
Venous thromboembolism (VTE): A blood clot forming in a vein, usually deep in the legs, which can travel to the lungs and cause a dangerous blockage. It is more common in people with cancer, because of the disease itself and some treatments. Read more

W

White blood cell: Blood cells that defend the body against infection and are made in the bone marrow. Chemotherapy may lower their number and raise the risk of infection. Read more
World Health Organization (WHO): The United Nations agency for health. It publishes international guidelines and classifications of diseases, including the official classification of tumour types.