Endometriosis does not directly cause cancer, but it is associated with a modestly increased risk of certain cancers, particularly specific types of ovarian cancer. The overall lifetime risk of ovarian cancer rises from about 1.3% in the general population to roughly 1.8% in women with endometriosis. That means fewer than two women out of every 100 with endometriosis will develop ovarian cancer. The risk is real but small, and leaving endometriosis untreated may matter more than most people realize.
The Link Between Endometriosis and Ovarian Cancer
Across large studies, women with endometriosis have roughly twice the risk of ovarian cancer compared to women without it. But that doubled risk applies unevenly. Endometriosis is most strongly tied to two uncommon subtypes of ovarian cancer: clear cell carcinoma and endometrioid carcinoma. These are not the most common forms of ovarian cancer, which is part of why the absolute numbers stay low.
A large study published in JAMA found that women with endometriosis had dramatically elevated risks for these specific subtypes. Clear cell ovarian cancer risk was about 11 times higher, endometrioid ovarian cancer about 8 times higher, and low-grade serous ovarian cancer about 8 times higher compared to women without endometriosis. Those multipliers sound alarming, but they apply to cancers that are individually rare, so the absolute risk remains modest.
A Dutch population-based study (the ENOCA cohort) confirmed these patterns, finding that the incidence of endometrioid and clear cell ovarian cancer was significantly higher in women with histologically confirmed endometriosis. After adjusting for detection bias, the risk was still roughly 2 to 2.5 times greater for each subtype.
How Endometriosis Could Lead to Cancer
Endometriosis and certain ovarian cancers share mutations in the same genes. Researchers have identified changes in genes called ARID1A, PIK3CA, and PTEN in both endometriotic tissue and in the cancers that sometimes develop from it. ARID1A mutations, for example, appear in up to 50% of clear cell ovarian cancers and 30% of endometrioid ovarian cancers. These genes normally act as brakes on cell growth. When they stop working, cells can begin dividing uncontrollably.
The current understanding is that endometriotic tissue accumulates these mutations over time. Most endometriosis never progresses beyond benign tissue. But in a small number of cases, enough mutations stack up in the right combination to trigger a malignant transformation. This is one reason why long-standing, untreated endometriosis is considered a greater concern than recently diagnosed disease. The longer abnormal tissue persists, the more opportunities it has to acquire dangerous genetic changes.
Endometriomas and Warning Signs
Endometriomas, the fluid-filled cysts that form on the ovaries in many women with endometriosis, deserve particular attention. Several characteristics raise concern for malignant transformation: the presence of solid tissue or papillary projections within the cyst, new blood vessel growth visible on ultrasound, and increasing size over time. Age also matters. Women over 45 and those who are postmenopausal face higher risk of an endometrioma becoming cancerous.
One documented case illustrates how slowly this can unfold. A woman had a small, 28-millimeter ovarian cyst that looked like a typical endometrioma on ultrasound in 2013. It remained stable and unremarkable through follow-up scans in 2017 and 2020. By the time it was eventually reassessed, it had grown into a 101-millimeter mass with multiple solid components. Pathology confirmed endometrioid cancer. Cases like this underscore the importance of continued monitoring, especially after menopause, even when an endometrioma appears stable and small.
One practical challenge is that endometriosis and ovarian cancer share symptoms like pelvic pain and elevated CA-125 levels on blood tests. Cancers that develop from endometriosis do tend to have some distinguishing features: they are more often found on one side only, detected at earlier stages, and less likely to produce fluid buildup in the abdomen compared to ovarian cancers unrelated to endometriosis. This earlier detection translates to generally better survival rates.
Cancers Beyond the Ovaries
Ovarian cancer gets the most attention, but endometriosis has been linked to elevated risk for other cancers as well. A large cohort study found that women with endometriosis had a 4.6 times higher risk of uterine cancer, a 2.5 times higher risk of ovarian cancer, and smaller increases in breast cancer risk (44% higher) and thyroid cancer risk (34% higher).
A comprehensive meta-analysis that pooled data from dozens of studies largely confirmed these patterns but painted a more conservative picture for some cancers. The pooled data showed a clear link with ovarian cancer (93% higher risk) and thyroid cancer (39% higher risk), while the association with breast cancer was minimal, only about 4% greater risk. There was no meaningful association with colorectal cancer, and the link with endometrial cancer was not statistically significant in the pooled analysis. Interestingly, endometriosis was associated with a lower risk of cervical cancer, roughly 32% lower than the general population.
Does Treating Endometriosis Reduce Cancer Risk?
This is perhaps the most important question for someone living with untreated endometriosis, and the evidence suggests the answer is yes. A population-based study found that surgical removal of the affected ovary reduced the risk of later ovarian cancer significantly, with an adjusted risk reduction of about 81%. Even when the ovaries were left in place, radical excision of all visible endometriotic tissue reduced ovarian cancer risk by about 70%.
These are striking numbers. They suggest that the endometriotic tissue itself is part of what drives the cancer risk, and removing it can meaningfully change the trajectory. This doesn’t mean every woman with endometriosis needs aggressive surgery. The decision depends on symptom severity, fertility goals, age, and individual risk factors. But it does suggest that “leaving it alone” carries a tradeoff that’s worth understanding.
Tubal ligation and hysterectomy have also shown protective effects against ovarian cancer in some studies, though these are obviously major decisions with implications well beyond cancer prevention.
Putting the Risk in Perspective
The relationship between endometriosis and cancer is real, supported by genetic evidence, large population studies, and a plausible biological mechanism. But it’s also important not to overstate it. The vast majority of women with endometriosis will never develop cancer from it. The lifetime risk of ovarian cancer with endometriosis is under 2%, and the absolute increases for other cancers are similarly small.
What the data does support is that endometriosis is not a condition to simply ignore. Long-standing, untreated disease, especially ovarian endometriomas in women approaching or past menopause, warrants regular imaging and follow-up. And for women already considering surgery for symptom relief, the potential cancer risk reduction is another factor worth weighing in that conversation.