Endometriosis and Cancer Risk: What the Evidence Shows

The short answer: Endometriosis is not cancer, and most women with it never develop cancer. Large studies show it is linked with a small rise in the chance of a few types of ovarian cancer, mainly clear-cell and endometrioid ovarian cancer, but the overall chance stays low. Experts do not advise routine cancer screening tests, or removing healthy ovaries, for this reason alone. This page explains what the research actually shows and what it cannot tell us. For a practical guide to which symptoms to report and when to get checked, see endometriosis and cancer risk: what every woman should know.

Does Endometriosis Cause Cancer?

Endometriosis — a condition where tissue similar to the womb lining (endometrium) grows outside the womb, often on the ovaries and the lining of the pelvis (see understanding endometriosis) — affects approximately 10% of women of reproductive age. The relationship between endometriosis and cancer is nuanced: endometriosis is not itself a cancer, but it is associated with an increased risk of certain ovarian cancer subtypes.

The Evidence

Large studies that compared thousands of women with and without endometriosis have found these links:

Clear-cell ovarian cancer — about 3 times more common in women with endometriosis
Endometrioid ovarian cancer — about 2 times more common
Low-grade serous ovarian cancer (a slow-growing type) — about 2 times more common
High-grade serous ovarian cancer (the most common type of ovarian cancer) and mucinous ovarian cancer — no clear link
Ovarian cancer overall — roughly 1.5 to 2 times the usual chance

These figures come mainly from a 2012 pooled analysis of 13 studies (Pearce and colleagues, Lancet Oncology) and a 2021 review that combined dozens of studies (Kvaskoff and colleagues, Human Reproduction Update); both are listed at the end of this page.

What “2 or 3 times” means in real life. These are relative risks: they compare one group of women with another. What matters to you is the absolute risk, your actual chance. In the general population, the lifetime chance of ovarian cancer is approximately 1.3%, roughly 1 woman in 75. Even if endometriosis nearly doubles that, the chance is still about 2 to 3 in 100, which means around 97 of every 100 women with endometriosis will never develop ovarian cancer. The higher “3 times” figure applies only to the rarer clear-cell type, not to ovarian cancer as a whole.

What the Studies Cannot Tell Us

A link is not proof of cause. The studies show that the two conditions occur together more often than expected; part of this may be explained by shared factors rather than endometriosis turning into cancer.
Many studies had weaknesses. The 2021 review found that a large share of the studies had a serious risk of bias (for example, in how endometriosis was recorded), so the true size of the risk is uncertain.
No clear link with womb-lining cancer. In the better-quality studies, endometriosis was not clearly linked to cancer of the womb lining (endometrial cancer).
Screening has not been shown to help. No study has shown that regular cancer screening tests benefit women with endometriosis, and the European endometriosis guideline (ESHRE, 2022) does not recommend routine cancer screening for them.

Endometriosis-Associated Ovarian Cancer (EAOC)

Doctors call the ovarian cancers linked with endometriosis “endometriosis-associated ovarian cancer” (EAOC). How they develop is not fully understood. The leading idea is that long-lasting inflammation inside chocolate cysts (endometriomas, cysts on the ovary filled with old blood) may, very rarely and over many years, lead to cell changes. Most chocolate cysts never change. A cyst is looked at more closely if it is growing, has solid parts on the scan, or appears or changes after menopause; our page on ovarian cysts explains what scan reports mean.

What Should Women With Endometriosis Do?

Do not panic — the absolute risk increase is small
Keep any chocolate cyst under review — your gynaecologist will advise how often to repeat the ultrasound; a cyst that grows, develops solid parts, or appears after menopause needs a closer look
Report new symptoms — bloating, feeling full quickly, pelvic or tummy pain, or needing to pass urine urgently that is new and happens on most days (more than 12 times a month), especially if it feels different from your usual endometriosis pain. The first tests are usually a pelvic ultrasound and a CA-125 blood test. Endometriosis itself often raises CA-125 (most labs treat below 35 U/mL as normal; check your report’s own range), so the result is read together with the scan
Know when a specialist helps — most women with endometriosis are looked after by their gynaecologist; a gynaecological oncologist becomes useful when a scan or blood test raises a concern. Removing healthy ovaries only to lower this small risk is not routinely advised

Treating endometriosis is about controlling pain and protecting fertility; our guide to endometriosis treatment options explains medicines and keyhole surgery. Whether treatment changes the small cancer risk is not yet clear.

Dr. Nishtha Tripathi Patel manages complex endometriosis and endometriosis-associated ovarian masses in Ahmedabad. Contact: +91 76988 00333.