A cancerous ovarian cyst usually has no typical symptom: most cysts and lumps of the ovary are found by chance during an examination or an ultrasound scan, not because of symptoms [1]. The symptoms to take seriously are those of ovarian cancer: pain in the pelvis or abdomen, bloating or a growing abdomen, feeling full quickly and needing to pass urine often, when they are new and happen on more than 12 days a month [10]. Fortunately, most ovarian cysts are benign [1]; what decides the risk is how the cyst looks on ultrasound, which is written on the ultrasound report as an O-RADS score [6, 8].
Key points
- Most ovarian cysts and lumps are benign and are often found by chance on an ultrasound scan [1].
- Functional cysts are common during the reproductive years, and most go away on their own within a few menstrual cycles [2].
- A simple cyst (fluid only, with a smooth wall) has a very low risk of cancer; in a study of nearly 3000 women aged 50 or over with simple cysts, none of these cysts became cancer [3].
- The appearance of the cyst on ultrasound is the most important clue: an irregular solid part, many small growths inside the cyst, a lot of blood flow and fluid in the abdomen make cancer more likely [5].
- On an ultrasound report, O-RADS 2 means almost certainly benign; O-RADS 4 and 5 mean that further tests and advice from a gynaecological cancer surgeon are needed [6, 7].
- The CA-125 blood test cannot show on its own whether a cyst is cancerous; the appearance of the cyst on ultrasound matters more [8].
Is an ovarian cyst cancer? Types of ovarian cysts and lumps
A cyst is a sac filled with fluid. An ovarian cyst is usually not cancer: most cysts and lumps of the ovary are benign [1]. A follicle (a small sac in which an egg grows) or a corpus luteum up to 3 cm is part of a normal ovary [7]. Sometimes these structures grow larger and are then called "functional cysts"; they are very common during the reproductive years [2].
| Type | What it means | What usually happens |
|---|---|---|
| Functional cyst | A cyst that forms during the normal cycle of ovulation | Most go away on their own within a few menstrual cycles [2] |
| Haemorrhagic cyst, endometrioma ("chocolate cyst") and dermoid cyst | Benign types whose appearance on ultrasound is well known | If they look typical, they are almost certainly benign [6]; a cyst that stays after a few menstrual cycles is often a non-functional type such as an endometrioma [2] |
| Borderline tumour | Abnormal cells that may become cancer, but usually do not [9] | It is removed with surgery, sometimes keeping the other ovary; the outlook is good, especially when it is found early [9] |
| Ovarian cancer | A malignant tumour | Surgery and usually chemotherapy; see further down the page |
The type of cyst is judged from how it looks on ultrasound, and sometimes it is only confirmed after surgery, when the tissue is examined.
Ovarian cancer symptoms vs ovarian cyst symptoms: is there a difference?
No single symptom shows that a cyst is cancerous. Most cysts and lumps of the ovary are found by chance during an examination or an ultrasound scan, not because of symptoms [1].
- Benign cysts sometimes cause sudden or on-and-off pain [1], for example when the cyst twists or bursts. These complications are uncommon: in a large study of women whose benign-looking lumps were only monitored, fewer than 1 in 100 had a twisted or burst cyst within 2 years [4].
- The symptoms of ovarian cancer are usually vague: pain in the pelvis or abdomen, bloating or a growing abdomen, feeling full quickly or difficulty eating, and needing to pass urine often or urgently. When these symptoms are new (less than a year) and happen on more than 12 days a month, they are worth checking [10].
So if you have a cyst and symptoms like these, tell your doctor; but the main decision is based on how the cyst looks on ultrasound. Read more: What are the symptoms of ovarian cancer?
Can an ovarian cyst turn into cancer?
A cyst that looks benign on ultrasound rarely becomes cancer:
- In a study in the United States of women aged 50 or over, nearly 3000 women had a simple cyst smaller than 10 cm. None of these cysts turned into cancer, and about 7 in 10 of the cysts went away on their own [3].
- In an international study of women with benign-looking lumps who were monitored instead of having surgery, about 4 in 1000 had cancer within 2 years, and in about 1 in 5 the lump went away on its own [4].
But if the appearance of a cyst changes during follow-up (for example, it develops an inner wall or a solid part), it needs to be checked again. In the same American study, the women who had earlier had a simple cyst and later developed cancer had either first developed a new change in the ovary, had their cyst disappear, or had cancer in the other ovary [3]. A cyst that does not go away after 2 to 3 menstrual cycles is usually not functional and often needs surgery [2].
The ultrasound report: O-RADS and worrying signs
| Score | What it means | Chance of cancer | Usual next step |
|---|---|---|---|
| O-RADS 0 | The assessment is incomplete | Not known | Repeat ultrasound or another test |
| O-RADS 1 | Normal ovary (a follicle or corpus luteum up to 3 cm) | Normal | Nothing needed |
| O-RADS 2 | Almost certainly benign, such as a simple cyst | Fewer than 1 in 100 | Depending on size and age: no follow-up or a repeat ultrasound |
| O-RADS 3 | Low risk | 1 to fewer than 10 in 100 | If it is not removed, repeat ultrasound; sometimes MRI; under the care of a gynaecologist |
| O-RADS 4 | Intermediate risk | 10 to fewer than 50 in 100 | Specialist ultrasound or MRI; a gynaecologist with advice from a gynaecological cancer surgeon |
| O-RADS 5 | High risk | 50 or more in 100 | Referral to a gynaecological cancer surgeon |
The details of follow-up depend on the size of the cyst and whether you have been through the menopause. The O-RADS score is interpreted together with age, symptoms and examination.
Signs seen more often in benign lumps [5]: a unilocular cyst (a single fluid-filled space); a very small solid part (less than 7 mm); an "acoustic shadow" behind the lump; a cyst with several spaces and smooth walls smaller than 10 cm; and no blood flow on Doppler ultrasound.
Signs that make cancer more likely [5]: a solid lump with an irregular shape; free fluid in the abdomen (ascites); at least 4 small growths on the inner wall of the cyst; an irregular lump with several spaces and solid parts measuring 10 cm or more; and a lot of blood flow on Doppler.
With these simple rules, about 3 in 4 lumps can be classified, and most of them are classified correctly [5]. An experienced ultrasound specialist gives the most accurate assessment; when one is not available, these models help. If the ultrasound is not conclusive, MRI is the next step [8].
What role do CA-125 and age play?
The CA-125 blood test is the best blood test to help assess an ovarian lump before surgery, but it is not useful for screening for ovarian cancer [8]. The appearance of the lump on ultrasound matters more than CA-125, and adding CA-125 to ultrasound models does not make them more accurate [8]. When the doctor suspects cancer, CA-125 helps [8]. Read more: I have an ovarian cyst; do I need a tumour marker test?
Age and family history also matter and affect decisions about an ovarian lump [1]. The "risk of malignancy index" (RMI) combines menopausal status, the appearance of the lump on ultrasound and CA-125; but newer ultrasound models are more accurate [8]. If ovarian or breast cancer runs in your family, tell your doctor. Read: Is cancer hereditary?
When is a cyst just monitored, and when is surgery needed?
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If it is a borderline tumour or cancer
A borderline tumour has a good outlook [9]. Read about the treatment of ovarian cancer and the chance of cure: Is ovarian cancer curable? and Ovarian cancer.
When should I contact a doctor?
Most ovarian cysts are harmless, but do not wait in these situations:
- Sudden, severe pain in the pelvis or abdomen; the cyst may have twisted or burst [1, 4]. Go to an emergency department straight away or call your local emergency number.
- Bloating, a growing abdomen, feeling full quickly, pelvic pain or needing to pass urine often that has started recently and happens on more than 12 days a month [10].
- An ultrasound report with O-RADS 4 or 5, or a lump with an irregular solid part or fluid in the abdomen: see a gynaecologist soon [5, 6].
- A cyst whose appearance has changed during follow-up, for example a new solid part or inner wall [3].
Frequently asked questions
What does O-RADS 4 mean? Does it mean I have cancer?
Is a complex ovarian cyst dangerous?
A "complex cyst" is a cyst that is not just clear fluid; for example, it has inner walls, blood, a solid part or small growths. Many of these cysts, such as haemorrhagic cysts, endometriomas ("chocolate cysts") or dermoid cysts, have a well-known appearance and are almost certainly benign [6]. The risk is decided by the type of these features, not by the word "complex"; this is why it is better for the ultrasound report to include an O-RADS score [5, 6].
Does the contraceptive pill make an ovarian cyst go away?
In eight studies of nearly 700 women, the contraceptive pill did not make functional cysts go away faster; most cysts went away without treatment within a few menstrual cycles [2]. Waiting 2 to 3 cycles and a repeat ultrasound is usually enough; a cyst that stays is usually not functional [2]. Read about the pill and cancer: Does the contraceptive pill cause cancer?
Is an ovarian cyst after the menopause dangerous?
A simple cyst after the menopause is also usually harmless: in a study of women aged 50 or over, no simple cyst smaller than 10 cm became cancer, and most went away on their own [3]. But age affects the decision [1], and a lump with a solid part needs a closer look after the menopause, as at any age [5, 6].
Is a borderline ovarian tumour cancer?
A borderline tumour has abnormal cells that may become cancer, but usually do not. Its outlook is good, especially when it is found early. At an early stage, women who want to have children can have only one ovary and fallopian tube, or part of an ovary, removed [9].
Does a high CA-125 mean my cyst is cancerous?
Not necessarily. CA-125 alone is not enough for a diagnosis, and the appearance of the cyst on ultrasound matters more [8]. Read: What does a high CA-125 mean?
If the cyst is cancerous, can it be treated?
The chance of curing ovarian cancer depends on its stage and type. Read: Is ovarian cancer curable?
IOTA rules, O-RADS and the natural history of adnexal masses (for doctors)
For physicians
IOTA Simple Rules. In 1066 patients with 1233 persistent adnexal masses (73% benign, 27% malignant), five M-rules (irregular solid tumour; ascites; at least 4 papillary structures; irregular multilocular-solid tumour with a largest diameter of 100 mm or more; very high colour content on colour Doppler) and five B-rules (unilocular cyst; solid components with a largest diameter of less than 7 mm; acoustic shadows; smooth multilocular tumour less than 100 mm; no detectable blood flow on Doppler) were defined. In prospective testing, the rules were applicable to 76% of masses (386 of 507), with a sensitivity of 95%, specificity of 91%, LR+ of 10.37 and LR− of 0.06; for masses that cannot be classified by these rules, an expert ultrasound examiner is helpful [5].
O-RADS US. Six categories: 0 incomplete evaluation, 1 normal ovary, 2 almost certainly benign (<1%), 3 low risk (1% to <10%), 4 intermediate risk (10% to <50%) and 5 high risk (≥50%), with a management recommendation for each category and alignment with the IOTA ADNEX model [6]. Version 2022 added new benign features (bilocular cysts without solid components and acoustic shadowing in smooth-contoured solid lesions); because O-RADS 4 is an appropriate cut-off for malignancy, O-RADS 3 lesions are followed with ultrasound if not excised, and MRI is emphasised as a supplemental evaluation for solid lesions and cystic lesions with solid components [7].
ESGO/ISUOG/IOTA/ESGE (2021). Subjective assessment by an expert (Level III) ultrasound examiner performs best; when one is not available, the IOTA Simple Rules risk model or ADNEX model is recommended, as they outperform the RMI and other morphological scoring systems and are superior to CA-125, HE4 and ROMA. CA-125 is the best single-protein biomarker for pre-operative characterisation but is not useful for screening and does not improve the performance of ultrasound models; HE4 and ROMA do not improve on CA-125 alone; MRI with functional sequences is a second-line tool after ultrasound [8].
Natural history. IOTA5 (1919 patients with a new mass that looked benign on ultrasound, managed conservatively; median follow-up 27 months): 2-year cumulative incidence of spontaneous resolution 20.2%, invasive malignancy 0.4%, borderline tumour 0.3%, torsion 0.4% and cyst rupture 0.2% [4]. In the Kentucky screening programme (15,106 asymptomatic women aged 50 or over), 2763 women (18%) had 3259 unilocular cysts smaller than 10 cm; 69.4% resolved spontaneously, 16.5% developed a septum, 5.8% developed a solid area and 6.8% persisted as unilocular lesions; no woman with an isolated unilocular cyst developed ovarian cancer [3]. In a Cochrane review (8 trials, 686 women), combined oral contraceptives did not hasten the resolution of functional cysts; waiting 2 to 3 cycles is appropriate, and persistent cysts tend to be pathological (endometrioma or para-ovarian cyst) [2].
Goff symptom index. Pelvic or abdominal pain, urinary urgency or frequency, increased abdominal size or bloating, and difficulty eating or feeling full, present for less than 1 year and occurring more than 12 times a month; sensitivity 56.7% for early-stage and 79.5% for advanced-stage disease, and specificity 90% in women over 50 and 86.7% in women under 50 [10].
Scientific evidence
Scientific evidence
1 itemDevelopment of an ovarian cancer symptom index
Related cancer types
Related questions
References
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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.
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