Key points
- Pembrolizumab (Keytruda) is an immunotherapy drug: it releases the brake (PD-1) that cancer puts on immune cells so the body can fight the cancer itself [1].
- It is used in many cancers, from melanoma and lung cancer to triple-negative breast, cervical and ovarian cancer [1].
- It is usually given as a 30-minute drip, once every 3 or every 6 weeks [1].
- In some cancers, tests such as PD-L1 or MSI must be done on a tumour sample before starting [1].
- The most important serious side effects are immune-related inflammation of the lungs, bowel, liver or glands, which can appear at any time, even after treatment ends; report any new symptom early [1] (immunotherapy side effects).
- Women should use reliable contraception during treatment and for 4 months after the last dose, and should not breastfeed [1].
What is this drug and how does it work?
For physicians
Pembrolizumab, brand name Keytruda, is a humanised IgG4 monoclonal antibody that blocks the PD-1 receptor [1]. It belongs to the "immune checkpoint inhibitors"; instead of attacking cancer cells directly, it works by helping the body's immune system [1].
T lymphocytes (a group of white blood cells) carry a receptor called PD-1 on their surface. Binding of the proteins PD-L1 and PD-L2 to this receptor inhibits T-cell proliferation and cytokine production. Some tumours increase these proteins and so escape immune surveillance [1]. Pembrolizumab binds to PD-1 and blocks its binding to PD-L1 and PD-L2; this releases the inhibition of the immune response, including the antitumour response [1].
This same activation of the immune system is also the main cause of the drug's side effects: the immune system may attack healthy organs and tissues too [1].
Which cancers is it used for?
According to the FDA label, pembrolizumab is approved alone or with chemotherapy, radiotherapy or other drugs, both in advanced cancers and before and after surgery in some early-stage cancers [1]. For some uses the tumour must be tested for PD-L1 expression (TPS or CPS score), MSI-H/dMMR or TMB-H with an FDA-approved test [1]. Approved uses may differ between countries.
Your doctor may prescribe this drug for:
- Melanoma [1, 2]
- Cutaneous squamous cell carcinoma [1]
- Merkel cell carcinoma [1]
- Non-small cell lung cancer [1, 3, 4]
- Malignant pleural mesothelioma [1]
- Head and neck cancer (squamous cell carcinoma) [1, 5]
- Classical Hodgkin lymphoma and primary mediastinal large B-cell lymphoma [1]
- MSI-H or dMMR solid tumours [1]
- TMB-H solid tumours (≥10 mutations per megabase) [1]
Whether it suits you depends on the type and stage of your cancer and your test results. Details of each use are in the section for doctors.
For physicians
| Cancer | Conditions of use | Key evidence |
|---|---|---|
| Melanoma | Unresectable or metastatic melanoma; adjuvant treatment after complete resection of stage IIB, IIC or III melanoma in adults and children aged 12 and over [1] | KEYNOTE-054 trial [2] |
| Cutaneous squamous cell carcinoma | Recurrent or metastatic disease, or locally advanced disease not curable by surgery or radiotherapy [1] | FDA label [1] |
| Merkel cell carcinoma | Recurrent locally advanced or metastatic disease (adults and children) [1] | FDA label [1] |
| Non-small cell lung cancer | First-line metastatic disease with chemotherapy (pemetrexed and platinum in non-squamous disease without EGFR or ALK alterations; carboplatin and paclitaxel or protein-bound paclitaxel in squamous disease); single agent in PD-L1-positive tumours (TPS ≥1%); before surgery with chemotherapy and then after surgery in resectable tumours (≥4 cm or node-positive); adjuvant after surgery and platinum chemotherapy in stage IB (T2a ≥4 cm), II or IIIA [1] | KEYNOTE-189 trial [3]; KEYNOTE-671 trial [4] |
| Malignant pleural mesothelioma | First line in unresectable advanced or metastatic disease, with pemetrexed and platinum chemotherapy [1] | FDA label [1] |
| Head and neck cancer (squamous cell carcinoma) | Resectable locally advanced disease with PD-L1 (CPS ≥1): before surgery, then with radiotherapy with or without cisplatin, then alone; first line in metastatic or unresectable recurrent disease with platinum and fluorouracil, or as a single agent with CPS ≥1; single agent after progression on or after platinum chemotherapy [1] | KEYNOTE-048 trial [5] |
| Classical Hodgkin lymphoma and primary mediastinal large B-cell lymphoma | Relapsed or refractory disease in adults, and in children under the conditions set out in the label [1] | FDA label [1] |
| MSI-H or dMMR solid tumours | Unresectable or metastatic tumours that progressed after prior treatment with no satisfactory alternative (adults and children) [1] | FDA label [1] |
| TMB-H solid tumours (≥10 mutations per megabase) | Unresectable or metastatic tumours after progression on prior treatment with no other satisfactory option; this use is based on accelerated approval [1] | FDA label [1] |
| Cancer | Conditions of use | Key evidence |
|---|---|---|
| Oesophageal cancer | Locally advanced or metastatic disease not amenable to surgery or definitive chemoradiotherapy: with platinum and fluoropyrimidine chemotherapy in PD-L1-positive tumours (CPS ≥1); or as a single agent after one or more lines in squamous disease with CPS ≥10 [1] | KEYNOTE-590 trial [9] |
| Gastric and gastro-oesophageal junction cancer (adenocarcinoma) | First line in unresectable locally advanced or metastatic disease with PD-L1 (CPS ≥1): with trastuzumab and chemotherapy in HER2-positive disease, and with fluoropyrimidine and platinum chemotherapy in HER2-negative disease [1] | KEYNOTE-859 trial [8] |
| MSI-H or dMMR colorectal cancer | Unresectable or metastatic disease [1] | KEYNOTE-177 trial [7] |
| Hepatocellular carcinoma | Hepatitis B-related hepatocellular carcinoma in patients previously treated with systemic therapy other than PD-1/PD-L1-containing regimens [1] | FDA label [1] |
| Biliary tract cancer | Unresectable locally advanced or metastatic disease, with gemcitabine and cisplatin [1] | FDA label [1] |
| Kidney cancer (renal cell carcinoma) | First line in advanced disease with axitinib or lenvatinib; adjuvant treatment at intermediate-high or high risk of recurrence after nephrectomy (or nephrectomy and resection of metastatic lesions), alone or with belzutifan in disease with a clear cell component [1] | KEYNOTE-426 trial [11] |
| Bladder and urinary tract (urothelial) cancer | Locally advanced or metastatic disease with enfortumab vedotin; single agent in patients not eligible for any platinum chemotherapy or after progression on it; muscle-invasive bladder cancer before and after cystectomy with enfortumab vedotin; high-risk BCG-unresponsive non-muscle-invasive bladder cancer with carcinoma in situ, in patients not undergoing cystectomy [1] | EV-302 (KEYNOTE-A39) trial [6] |
| Cervical cancer | Locally advanced disease (FIGO 2014 stage III to IVA) with chemoradiotherapy; persistent, recurrent or metastatic disease with PD-L1 (CPS ≥1) with chemotherapy with or without bevacizumab; single agent after progression on chemotherapy with CPS ≥1 [1] | KEYNOTE-A18 trial [10] |
| Endometrial cancer | Primary advanced or recurrent disease with carboplatin and paclitaxel, then alone; advanced pMMR or non-MSI-H disease with lenvatinib after prior systemic therapy; advanced MSI-H or dMMR disease as a single agent after prior systemic therapy [1] | FDA label [1] |
| Ovarian cancer | Platinum-resistant epithelial ovarian, fallopian tube or primary peritoneal carcinoma with PD-L1 (CPS ≥1) after one or two prior regimens, with paclitaxel with or without bevacizumab [1] | FDA label [1] |
| Triple-negative breast cancer | High-risk early disease: with chemotherapy before surgery and then alone after surgery; locally recurrent unresectable or metastatic disease with PD-L1 (CPS ≥10) with chemotherapy, or first line with sacituzumab govitecan [1] | KEYNOTE-522 trial [12] |
A summary of the FDA label (July 2026 revision); the exact details of each use, age limits and required tests are in the full label.
How it is given and dose
Show detailsHide
Treatment regimens and doses: index12 regimens
Pembrolizumab is given in hospital or at a treatment centre as an intravenous drip over about 30 minutes [1]. In adults it is usually given once every 3 weeks or every 6 weeks depending on the dose, and in children once every 3 weeks [1]. If you are also having chemotherapy, in most regimens pembrolizumab is given on the same day, before the chemotherapy [1].
Length of treatment depends on the type and stage of cancer: as adjuvant treatment after surgery for melanoma, lung or kidney cancer, up to 12 months; in many uses for advanced disease, until the disease progresses, side effects become intolerable or up to 24 months [1].
Tests: before starting and regularly during treatment, blood tests check liver enzymes, creatinine (kidney function) and thyroid function [1]. In women who could become pregnant, pregnancy status is checked before starting [1]. In triple-negative breast cancer, when the drug is given before surgery, blood cortisol is also measured at the start, before surgery and when needed [1]. If you miss an infusion appointment, contact your treatment team as soon as possible to arrange a new time [1].
Before starting: PD-L1 (TPS or CPS), MSI/dMMR, TMB or HER2 testing with an approved test depending on the indication; liver enzymes, creatinine and thyroid function; pregnancy status [1].
Administration: dilute to 1 to 10 mg/mL in 0.9% sodium chloride or 5% dextrose; infuse over 30 minutes through a 0.2 to 5 micron low-protein-binding filter; do not give other drugs through the same line. Premedication is not routinely needed. Grade 1 or 2 infusion reaction: interrupt or slow the rate; grade 3 or 4: stop permanently [1].
Dose adjustment (dose reduction is not recommended) [1]:
- General rule: grade 3 immune-mediated adverse reaction, withhold; grade 4, recurrent grade 3 needing systemic immunosuppression, or inability to taper prednisone to 10 mg a day or less within 12 weeks: stop permanently.
- Pneumonitis: grade 2 withhold; grade 3 to 4 stop permanently. Colitis: grade 2 to 3 withhold; grade 4 stop permanently. Myocarditis grade 2 to 4: stop permanently. Neurological toxicities: grade 2 withhold; grade 3 to 4 stop permanently.
- Hepatitis without tumour involvement of the liver: AST/ALT above 3 to 8 × ULN or bilirubin above 1.5 to 3 ×, withhold; AST/ALT above 8 × or bilirubin above 3 ×, stop permanently. With liver involvement: baseline 1 to 3 × rising to 5 to 10 ×, or baseline 3 to 5 × rising to 8 to 10 ×, withhold; above 10 × or bilirubin above 3 ×, stop permanently.
- Nephritis: grade 2 to 3 creatinine rise withhold, grade 4 stop permanently. Grade 3 to 4 endocrinopathy: withhold until clinically stable or stop depending on severity (hormone replacement). SJS/TEN/DRESS: suspected, withhold; confirmed, stop permanently.
- When withheld, give corticosteroids (prednisone 1 to 2 mg/kg a day or equivalent) until improvement to grade 1 or less, then taper over at least 1 month; resume after recovery to grade 0 to 1.
Monitoring: liver enzymes, creatinine and thyroid function at baseline and periodically; blood glucose and signs of adrenal insufficiency and hypophysitis; respiratory, gastrointestinal, skin, cardiac and neurological symptoms. Immune-mediated adverse reactions can occur months after the drug is stopped [1].
For physicians
Standard doses and combination regimens (FDA label)
Single agent in advanced disease
Advanced melanoma; NSCLC with PD-L1 (TPS 1% or more); HNSCC; urothelial; MSI-H/dMMR (including colorectal and endometrial); oesophageal; cervical; HCC; Merkel; TMB-H; cSCC; cHL and PMBCL; BCG-unresponsive NMIBCCycle length: Every 3 or 6 weeks
Advanced melanoma; NSCLC with PD-L1 (TPS 1% or more); HNSCC; urothelial; MSI-H/dMMR (including colorectal and endometrial); oesophageal; cervical; HCC; Merkel; TMB-H; cSCC; cHL and PMBCL; BCG-unresponsive NMIBC
Before prescribing: Prescribing notes| Drug | Dose | Route | Schedule |
|---|---|---|---|
| Pembrolizumab | 200 mg every 3 weeks or 400 mg every 6 weeks | IV infusion over 30 minutes | Day 1 |
| Children (cHL, PMBCL, MSI-H, Merkel, TMB-H) | |||
| Pembrolizumab | 2 mg/kg (maximum 200 mg) | IV infusion over 30 minutes | Every 3 weeks |
[1]
Single-agent adjuvant treatment
Resected stage IIB, IIC or III melanoma (from age 12); stage IB (T2a 4 cm or more) to IIIA NSCLC after surgery and platinum chemotherapy; high-risk RCC after nephrectomyCycle length: Every 3 or 6 weeks
Resected stage IIB, IIC or III melanoma (from age 12); stage IB (T2a 4 cm or more) to IIIA NSCLC after surgery and platinum chemotherapy; high-risk RCC after nephrectomy
Before prescribing: Prescribing notes| Drug | Dose | Route | Schedule |
|---|---|---|---|
| Pembrolizumab | 200 mg every 3 weeks or 400 mg every 6 weeks | IV infusion over 30 minutes | Day 1 |
| Children aged 12 and over (melanoma) | |||
| Pembrolizumab | 2 mg/kg (maximum 200 mg) | IV | Every 3 weeks |
[1]
Subcutaneous form (Keytruda Qlex)
Adults and children aged 12 and over weighing more than 40 kg, in solid tumour indications (not cHL or PMBCL)Cycle length: Every 3 or 6 weeks
Adults and children aged 12 and over weighing more than 40 kg, in solid tumour indications (not cHL or PMBCL)
Before prescribing: Prescribing notes| Drug | Dose | Route | Schedule |
|---|---|---|---|
| Every 3 weeks | |||
| Pembrolizumab + berahyaluronidase alfa | 395 mg / 4800 units (2.4 mL) | Subcutaneous in the thigh or abdomen, over 1 minute | Day 1 |
| Every 6 weeks | |||
| Pembrolizumab + berahyaluronidase alfa | 790 mg / 9600 units (4.8 mL) | Subcutaneous, over 2 minutes | Day 1 |
Its dose and administration differ from the IV form; do not give intravenously; avoid the 5 cm around the navel; to be given by healthcare staff only [13].
First-line metastatic NSCLC + chemotherapy
Non-squamous without EGFR/ALK (KEYNOTE-189); squamous (KEYNOTE-407)Cycle length: Every 21 days
Non-squamous without EGFR/ALK (KEYNOTE-189); squamous (KEYNOTE-407)
Before prescribing: Prescribing notes| Drug | Dose | Route | Schedule |
|---|---|---|---|
| Non-squamous, 4 cycles | |||
| Pembrolizumab | 200 mg every 3 weeks or 400 mg every 6 weeks | IV infusion over 30 minutes | Day 1 |
| Pemetrexed + cisplatin or carboplatin | 500 mg/m² + 75 mg/m² or AUC 5 | IV, after pembrolizumab | Day 1 every 21 days; then maintenance pembrolizumab + pemetrexed 500 every 3 weeks |
| Squamous, 4 cycles | |||
| Carboplatin + paclitaxel (or nab-paclitaxel) | AUC 6 + 200 mg/m² (or 100 mg/m²) | IV | Day 1 (nab-paclitaxel days 1, 8 and 15) every 21 days; then pembrolizumab alone |
Chemotherapy doses as described for the trials in the label; pembrolizumab on the same day before chemotherapy [1].
First-line metastatic or recurrent HNSCC (KEYNOTE-048)
Unresectable; with chemotherapy (or as a single agent with CPS 1 or more)Cycle length: Every 3 weeks
Unresectable; with chemotherapy (or as a single agent with CPS 1 or more)
Before prescribing: Prescribing notes| Drug | Dose | Route | Schedule |
|---|---|---|---|
| Pembrolizumab | 200 mg every 3 weeks or 400 mg every 6 weeks | IV infusion over 30 minutes | Day 1 |
| Up to 6 cycles | |||
| Cisplatin or carboplatin + fluorouracil | 100 mg/m² or AUC 5 + 1000 mg/m²/day | IV; fluorouracil as a continuous 96-hour infusion | Every 3 weeks |
Evidence: KEYNOTE-048 (2025), KEYNOTE-048 (2019)
First-line HER2-negative gastric/GEJ and oesophageal cancer + chemotherapy
CPS 1 or more; KEYNOTE-859 and KEYNOTE-590Cycle length: Every 3 weeks
CPS 1 or more; KEYNOTE-859 and KEYNOTE-590
Before prescribing: Prescribing notes| Drug | Dose | Route | Schedule |
|---|---|---|---|
| Pembrolizumab | 200 mg every 3 weeks or 400 mg every 6 weeks | IV infusion over 30 minutes | Day 1 |
| Cisplatin + fluorouracil | 80 mg/m² (day 1) + 800 mg/m²/day (days 1 to 5) | IV | Every 3 weeks (cisplatin up to 6 cycles in KEYNOTE-590) |
| Gastric option | |||
| CAPOX: oxaliplatin + capecitabine | 130 mg/m² + 1000 mg/m² twice a day | IV / oral | Day 1 / days 1 to 14, every 3 weeks |
Evidence: KEYNOTE-859 (2023), KEYNOTE-590 (2021)
Urothelial + enfortumab vedotin
Advanced or metastatic (EV-302); muscle-invasive bladder cancer before and after cystectomyCycle length: Every 3 or 6 weeks
Advanced or metastatic (EV-302); muscle-invasive bladder cancer before and after cystectomy
Before prescribing: Prescribing notes| Drug | Dose | Route | Schedule |
|---|---|---|---|
| Pembrolizumab | 200 mg every 3 weeks or 400 mg every 6 weeks | IV infusion over 30 minutes, after enfortumab vedotin on the same day | Day 1 |
| Muscle-invasive, cisplatin-eligible | |||
| Pembrolizumab | Before surgery 4 doses of 200 (or 2 doses of 400); after surgery 13 doses of 200 (or 7 doses of 400) | IV | Every 3 (or 6) weeks |
| Muscle-invasive, cisplatin-ineligible | |||
| Pembrolizumab | Before surgery 3 doses of 200; after surgery 14 doses of 200 (or 7 doses of 400) | IV | Every 3 (or 6) weeks |
Enfortumab vedotin dose as in its own label. Cisplatin ineligibility: CLcr below 60, ECOG 2 or more, grade 2 or higher hearing loss or neuropathy, or NYHA class III or higher heart failure [1, 6].
Evidence: EV-302 (KEYNOTE-A39) (2024)
Combination with oral targeted drugs
Advanced RCC (KEYNOTE-426 / CLEAR); pMMR endometrial (with lenvatinib); adjuvant ccRCC (with belzutifan)Cycle length: Every 3 or 6 weeks
Advanced RCC (KEYNOTE-426 / CLEAR); pMMR endometrial (with lenvatinib); adjuvant ccRCC (with belzutifan)
Before prescribing: Prescribing notes| Drug | Dose | Route | Schedule |
|---|---|---|---|
| Pembrolizumab | 200 mg every 3 weeks or 400 mg every 6 weeks | IV infusion over 30 minutes | Day 1 |
| RCC | |||
| Axitinib | 5 mg twice a day (escalation at intervals of 6 weeks or more can be considered) | Oral | Daily |
| RCC or endometrial | |||
| Lenvatinib | 20 mg once a day | Oral | Daily |
| Adjuvant ccRCC | |||
| Belzutifan | 120 mg once a day | Oral | Daily |
With axitinib: ALT/AST 3 to less than 10 × ULN without bilirubin 2 ×, withhold both drugs until grade 0 to 1 (consider corticosteroids); ALT/AST above 3 × with bilirubin 2 × or more, or 10 × or more: stop both permanently [1, 11].
Evidence: KEYNOTE-426 (2019)
Doses follow the trial protocol, guideline or official drug label (source given in the notes of each regimen). Before prescribing, check blood counts, renal and hepatic function, drug interactions and the patient’s condition, and adjust the dose according to the drug label.
Early stages: before and after surgery or with chemoradiotherapy (FDA label)
Resectable NSCLC, before and after surgery (KEYNOTE-671)
Resectable stage II, IIIA or IIIB (N2)Cycle length: Every 21 days
Resectable stage II, IIIA or IIIB (N2)
Before prescribing: Prescribing notes| Drug | Dose | Route | Schedule |
|---|---|---|---|
| Before surgery, 4 cycles | |||
| Pembrolizumab | 200 mg | IV infusion over 30 minutes | Day 1 |
| Cisplatin + pemetrexed or gemcitabine | 75 mg/m² + 500 mg/m² (day 1) or 1000 mg/m² (days 1 and 8) | IV | Every 21 days |
| After surgery | |||
| Pembrolizumab | 200 mg every 3 weeks or 400 mg every 6 weeks | IV infusion over 30 minutes | Day 1 |
Evidence: KEYNOTE-671 (2026), KEYNOTE-671 (2024)
Resectable locally advanced HNSCC with CPS 1 or more (KEYNOTE-689)
Resectable stage III to IVACycle length: Every 3 weeks
Resectable stage III to IVA
Before prescribing: Prescribing notes| Drug | Dose | Route | Schedule |
|---|---|---|---|
| Before surgery | |||
| Pembrolizumab | 200 mg | IV infusion over 30 minutes | 2 cycles every 3 weeks (6 weeks) |
| After surgery, with radiotherapy | |||
| Pembrolizumab | 200 mg | IV infusion over 30 minutes | 3 cycles every 3 weeks |
| With high-risk pathology | |||
| Cisplatin with radiotherapy | 100 mg/m² | IV, after pembrolizumab | Every 3 weeks, 3 cycles |
| Maintenance | |||
| Pembrolizumab | 200 mg | IV infusion over 30 minutes | Every 3 weeks for up to 12 cycles |
High-risk pathology: positive margin of less than 1 mm or extranodal extension [1].
Evidence: KEYNOTE-689 / NIVOPOSTOP (2025), KEYNOTE-689 (2025)
Locally advanced cervical cancer + chemoradiotherapy (KEYNOTE-A18)
FIGO 2014 stage III to IVA
FIGO 2014 stage III to IVA
Before prescribing: Prescribing notes| Drug | Dose | Route | Schedule |
|---|---|---|---|
| With chemoradiotherapy | |||
| Pembrolizumab | 200 mg | IV infusion over 30 minutes | Every 3 weeks, 5 cycles |
| With radiotherapy | |||
| Cisplatin | 40 mg/m² | IV | Weekly, 5 cycles (a sixth is optional) |
| After chemoradiotherapy | |||
| Pembrolizumab | 400 mg | IV infusion over 30 minutes | Every 6 weeks, 15 cycles |
Evidence: KEYNOTE-A18 (ENGOT-cx11/GOG-3047) (2024)
High-risk early triple-negative breast cancer (KEYNOTE-522)
Before and after surgeryCycle length: Every 21 days
Before and after surgery
Before prescribing: Prescribing notes| Drug | Dose | Route | Schedule |
|---|---|---|---|
| Before surgery, cycles 1 to 4 | |||
| Pembrolizumab | 200 mg every 3 weeks | IV infusion over 30 minutes | Day 1 |
| Cycles 1 to 4 | |||
| Paclitaxel + carboplatin | 80 mg/m² weekly + AUC 5 every 3 weeks (or AUC 1.5 weekly) | IV | Days 1, 8 and 15 |
| Cycles 5 to 8 | |||
| Doxorubicin (or epirubicin) + cyclophosphamide + pembrolizumab | 60 (or 90) + 600 mg/m² + 200 mg | IV | Day 1 every 3 weeks |
| After surgery | |||
| Pembrolizumab | 200 mg every 3 weeks (or 400 every 6 weeks) | IV infusion over 30 minutes | Day 1 |
Patients whose disease progressed on treatment before surgery, or who had unacceptable toxicity from pembrolizumab, should not receive treatment after surgery. Blood cortisol at baseline, before surgery and as needed [1, 12].
Evidence: KEYNOTE-522 (2024), KEYNOTE-522 (2020)
Before prescribing, check each dose against the drug label, laboratory tests and the patient’s condition.
Side effects
The most common side effects:
- Tiredness, muscle and joint pain, skin rash and itching, diarrhoea, nausea and cough [1].
- Fever, poor appetite, shortness of breath and constipation [1].
- An underactive thyroid (tiredness, feeling cold, weight gain), which is treated with thyroid tablets [1].
- White patches on the skin in some patients with melanoma [1].
- When it is given with chemotherapy, hair loss, vomiting, mouth sores and numbness in the hands and feet are also common [1].
For physicians
According to the FDA label, the most common side effects of pembrolizumab alone (reported in 20% or more of patients) are: fatigue, musculoskeletal pain, rash, diarrhoea, fever, cough, decreased appetite, itching, shortness of breath, constipation, pain, abdominal pain, nausea and hypothyroidism [1].
When the drug is given with chemotherapy or chemoradiotherapy, the list of common side effects is wider and also includes vomiting, hair loss, peripheral neuropathy (tingling and numbness in the hands and feet), mucosal inflammation and mouth sores [1]. As an example, the table below shows the frequency of some side effects in the KEYNOTE-006 trial, in which 555 patients with advanced melanoma received single-agent pembrolizumab [1]. Report any new or worsening symptom to your treatment team [1].
| Side effect | All grades | Grade 3 to 4 |
|---|---|---|
| Fatigue | 28% [1] | 0.9% [1] |
| Diarrhoea | 26% [1] | — |
| Rash | 24% [1] | 0.2% [1] |
| Nausea | 21% [1] | — |
| Joint pain | 18% [1] | 0.4% [1] |
| Itching | 17% [1] | — |
| Cough | 17% [1] | 0% [1] |
| Decreased appetite | 16% [1] | 0.5% [1] |
| Headache | 14% [1] | 0.2% [1] |
| Vitiligo (white patches on the skin) | 13% [1] | 0% [1] |
"—" means the label does not report a separate grade 3 to 4 frequency for this side effect. Frequencies differ in other cancers and combinations.
Serious side effects
Immunotherapy sometimes turns the immune system against healthy organs too. These side effects can appear at any time, even after treatment ends, and early treatment (usually with steroids) is important [1] (immunotherapy side effects):
- Lungs: a new cough, shortness of breath or chest pain [1].
- Bowel: diarrhoea, abdominal pain or blood in the stool [1].
- Liver: yellowing of the skin or eyes, dark urine [1].
- Glands: severe tiredness, dizziness, severe headache, thirst and passing a lot of urine [1].
- Kidneys, skin, heart, nerves and eyes: passing less urine, blisters or a widespread rash, palpitations, muscle weakness, blurred vision [1].
- Reactions during the infusion, and harm to an unborn baby [1].
For physicians
The most important risk of pembrolizumab is immune-mediated adverse reactions: the activated immune system can attack any organ or tissue; these reactions can be severe or fatal, involve several organs at once and appear even after treatment is stopped [1]. Early recognition and treatment (usually with corticosteroids or hormone replacement) is very important [1]. The frequencies below are from 2799 patients who received single-agent pembrolizumab in clinical trials [1]:
- Pneumonitis (lung inflammation): 3.4%; more common in patients who have had previous chest radiotherapy [1].
- Colitis (inflammation of the large bowel), which can present with diarrhoea: 1.7% [1].
- Immune-mediated hepatitis: 0.7%; in combination with axitinib, grade 3 and 4 ALT increases were seen in 20% and AST increases in 13% of patients [1].
- Thyroid disorders: hypothyroidism 8%, hyperthyroidism 3.4% and thyroiditis 0.6%; most patients with hypothyroidism needed long-term thyroid hormone [1].
- Other endocrine disorders: adrenal insufficiency 0.8%, hypophysitis (inflammation of the pituitary gland) 0.6% and type 1 diabetes, which may present with ketoacidosis, 0.2% [1].
- Nephritis (kidney inflammation) 0.3% and immune-mediated skin reactions 1.4%; severe skin reactions such as Stevens-Johnson syndrome, DRESS and TEN have been reported with drugs in this class [1].
- Rarer reactions (generally below 1%) such as myocarditis (inflammation of the heart muscle), myasthenia gravis, Guillain-Barré syndrome, encephalitis, uveitis (inflammation inside the eye) and pancreatitis [1].
- Severe infusion reactions, including anaphylaxis: 0.2% [1].
Pembrolizumab can harm a fetus [1]. The FDA label for this drug has no boxed warning [1].
When should I call my doctor?
If you have any of the following new or worsening symptoms, contact your doctor or treatment team straight away, even if your treatment has finished [1]:
- A new or worsening cough, chest pain or shortness of breath [1]
- Diarrhoea or more frequent bowel movements, black tarry stools or stools with blood or mucus, or severe abdominal pain [1]
- Yellowing of the skin or the whites of the eyes, severe nausea or vomiting, pain on the right side of the abdomen, dark (tea-coloured) urine, or easy bleeding and bruising [1]
- A persistent or unusual headache, eye sensitivity to light, palpitations, heavy sweating, extreme tiredness, weight change, excessive thirst or hunger, passing a lot of urine, dizziness or fainting [1]
- Passing less urine, blood in the urine or swollen ankles [1]
- A rash, itching, blistering or peeling skin, or painful sores in the mouth, nose, throat or genital area [1]
- An irregular heartbeat, confusion, a stiff neck, balance problems, double or blurred vision, or severe muscle pain and weakness [1]
- During the infusion: chills, itching or rash, flushing, shortness of breath or wheezing, dizziness, feeling faint, fever or back pain [1]
In severe cases (such as severe shortness of breath, severe chest pain or reduced consciousness), call your local emergency number.
Interactions, pregnancy and precautions
Drug interactions: the FDA label for pembrolizumab has no section on drug interactions [1]; even so, tell your doctor about all your medicines, including over-the-counter medicines, vitamins and herbal supplements [1].
Before starting treatment, tell your doctor if you have an autoimmune disease (such as Crohn's disease, ulcerative colitis or lupus), have had an organ or tissue transplant (including a cornea), a stem cell transplant from a donor, previous chest radiotherapy, or a nerve disease such as myasthenia gravis or Guillain-Barré syndrome [1].
Pregnancy and contraception: pembrolizumab may harm an unborn baby. Pregnancy status is checked before starting, and women who could become pregnant should use effective contraception during treatment and for 4 months after the last dose [1]. If you become pregnant or think you might be, tell your treatment team straight away [1].
Breastfeeding: do not breastfeed during treatment and for 4 months after the last dose [1].
Fertility: no studies have been done on the effect of pembrolizumab on fertility [1]; if you are planning to have children, talk to your doctor before starting treatment.
Vaccines: the FDA label gives no specific advice about vaccination during treatment [1]; talk to your treatment team before any vaccination.
Stem cell transplant and multiple myeloma: allogeneic (donor) haematopoietic stem cell transplantation before or after treatment with this class of drugs may be associated with serious or fatal complications such as graft-versus-host disease and hepatic veno-occlusive disease [1]. Adding pembrolizumab to thalidomide analogues and dexamethasone in multiple myeloma increased mortality and is not recommended outside a clinical trial [1].
Frequently asked questions
Is pembrolizumab chemotherapy?
Does Keytruda cause hair loss?
Hair loss is not in the list of common side effects of pembrolizumab alone in the FDA label, but when it is given with chemotherapy or chemoradiotherapy, it is reported as a common side effect [1].
Can side effects appear after treatment ends?
Yes. Immune-related side effects usually appear during treatment, but they can also appear after the drug is stopped; so tell your doctor about new symptoms even after treatment has ended [1].
Can every patient with these cancers have Keytruda?
No. Each use has specific conditions (type and stage of cancer, previous treatments), and for some uses tumour marker tests such as PD-L1, MSI-H/dMMR or TMB-H must be done [1]. Your doctor decides whether the drug is suitable based on these conditions.
Scientific evidence
Show detailsHide
Key studies
10 itemsPembrolizumab Plus Pemetrexed and Platinum in Nonsquamous Non–Small-Cell Lung Cancer: 5-Year Outcomes From the Phase 3 KEYNOTE-189 Study
Pembrolizumab or placebo with chemoradiotherapy followed by pembrolizumab or placebo for newly diagnosed, high-risk, locally advanced cervical cancer (ENGOT-cx11/GOG-3047/KEYNOTE-A18): overall survival results from a randomised, double-blind, placebo-controlled, phase 3 trial
Adjuvant Pembrolizumab versus Placebo in Resected Stage III Melanoma
Neoadjuvant pembrolizumab plus chemotherapy followed by adjuvant pembrolizumab compared with neoadjuvant chemotherapy alone in patients with early-stage non-small-cell lung cancer (KEYNOTE-671): a randomised, double-blind, placebo-controlled, phase 3 trial
Pembrolizumab alone or with chemotherapy versus cetuximab with chemotherapy for recurrent or metastatic squamous cell carcinoma of the head and neck (KEYNOTE-048): a randomised, open-label, phase 3 study
Pembrolizumab in Microsatellite-Instability-High Advanced Colorectal Cancer
Pembrolizumab plus chemotherapy versus placebo plus chemotherapy for HER2-negative advanced gastric cancer (KEYNOTE-859): a multicentre, randomised, double-blind, phase 3 trial
Pembrolizumab for Early Triple-Negative Breast Cancer
Pembrolizumab plus Axitinib versus Sunitinib for Advanced Renal-Cell Carcinoma
Enfortumab Vedotin and Pembrolizumab in Untreated Advanced Urothelial Cancer
Related cancer types
Treatment regimens (physicians)
References
13 referencesShow all references, 11 with a study cardClose the reference list
Numbers in the text, such as [1], refer to these sources. Sources with a “Study card” button are summarised in the site’s evidence library.
- 1KEYTRUDA (pembrolizumab) injection, for intravenous use: Prescribing InformationSource Back to text: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145
- 2Adjuvant Pembrolizumab versus Placebo in Resected Stage III Melanoma
- 3Pembrolizumab Plus Pemetrexed and Platinum in Nonsquamous Non–Small-Cell Lung Cancer: 5-Year Outcomes From the Phase 3 KEYNOTE-189 Study
- 4
- 5
- 6Enfortumab Vedotin and Pembrolizumab in Untreated Advanced Urothelial Cancer
- 7Pembrolizumab in Microsatellite-Instability-High Advanced Colorectal Cancer
- 8Pembrolizumab plus chemotherapy versus placebo plus chemotherapy for HER2-negative advanced gastric cancer (KEYNOTE-859): a multicentre, randomised, double-blind, phase 3 trial
- 9Pembrolizumab plus chemotherapy versus chemotherapy alone for first-line treatment of advanced oesophageal cancer (KEYNOTE-590): a randomised, placebo-controlled, phase 3 study
- 10Pembrolizumab or placebo with chemoradiotherapy followed by pembrolizumab or placebo for newly diagnosed, high-risk, locally advanced cervical cancer (ENGOT-cx11/GOG-3047/KEYNOTE-A18): overall survival results from a randomised, double-blind, placebo-controlled, phase 3 trial
- 11Pembrolizumab plus Axitinib versus Sunitinib for Advanced Renal-Cell Carcinoma
- 12Pembrolizumab for Early Triple-Negative Breast Cancer
- 13KEYTRUDA QLEX (pembrolizumab and berahyaluronidase alfa-pmph) injection, for subcutaneous use: Prescribing Information
This page is based on reputable scientific sources and was last updated on 27 October 2026. The content of this website is for educational and informational purposes only and does not replace consultation, diagnosis or treatment by a specialist physician. Consult your treating physician about any treatment decision.
Printed from the website; the full and up-to-date version: https://drdabiri.com/en/drugs/pembrolizumab/