Understanding the Connection between Endometriosis and Cancer Risk

Endometriosis and cancer are very different conditions, but unfortunately, they share some connections. Endometriosis is a benign, painful condition where the tissue that resembles the internal lining of the uterus grows outside of it inside your abdomen and pelvis (and sometimes beyond), causing inflammation and scarring. That reaction causes pain and usually impacts fertility as well. On the other hand, cancer is an uncontrolled malignant growth of abnormal cells that can spread throughout the body and kill.

While endometriosis is not cancerous, it can still act like cancer by directly invading tissues and organs or spreading through the lymphatic and blood systems. Research suggests that there may be molecular links between endometriosis and certain types of cancer, rooted in genetics and epigenetics (the study of how your environment turns genes on and off). Here’s what you need to know.

The overall endometriosis and cancer risk of developing cancer of different types seems to be slightly increased in women with endometriosis. Additional studies point to increased cancer risk in patients with the closely related condition of adenomyosis. The reasons for this are unclear, although molecular connections are being uncovered, and the risk differs by cancer type. 

Endometriosis and Cancer Risk Transformation

Endometriosis cells themselves can directly transform or degenerate into cancer. The specific types are clear cell, endometrioid, and, more rarely, stromal sarcoma. No one knows the exact percentage because of the under-reporting of both endometriosis and these cancer transformation events. However, the estimation is only a fraction of 1%. This transformation is a tiny percentage, but if you consider that millions of women have endometriosis, even a tiny percentage means tens of thousands of women may be at risk. 

Endometriosis and Cancer Risk for Ovarian

Endometriosis has been linked to an increased risk of developing certain types of ovarian cancer. Studies have found that women with endometriosis are more likely to develop clear cell and endometrioid ovarian cancers than women without the condition. In fact, the risk is estimated to be between 1.5 to 3 times higher in women with endometriosis. The risk is highest when endometriosis significantly involves the ovaries, such as the presence of endometriomas. 

The reasons for this link are not entirely clear. Still, it is thought that the inflammation and scarring caused by endometriosis may increase the risk of cancerous mutations or epigenetic events in the cells. It’s important to note that while the risk has increased, most women with endometriosis will not develop ovarian cancer. However, just as with direct malignant transformation, a small percentage of millions of women with endo can still mean thousands to tens of thousands of women can be affected.  

Endometriosis and Thyroid Cancer

A smaller but statistically significant 1.4-fold higher risk for thyroid cancer has been consistently reported in multiple studies. The reason for this is unknown, but some researchers suggest this link may be based on autoimmunity disorders, which can be shared between endometriosis, thyroid disease, and cancer.

Endometriosis and Breast Cancer

There is also some evidence to suggest that there may be a tiny link between endometriosis and breast cancer, amounting to only about 4% increased risk. Other studies point to a somewhat higher risk. However, this link is not as well established as the link between endometriosis and ovarian cancer, and more research is needed to confirm it.

Endometriosis and Cervical Cancer

Unlike ovarian and breast cancer, there is no clear link between endometriosis and cervical cancer. In fact, a handful of studies suggest that there may be a reduced risk of cervical cancer in women with endometriosis. The reason for this is unknown. 

Endometriosis and Cancer Risk

While one might think there may be an association with uterine endometrial cancer, this may or may not be the case. A recent meta-analysis (review of multiple studies) suggested no risk, while other studies have reported a significantly increased risk of endometrial cancer in women with endometriosis and adenomyosis. 

Similarly, there is conflicting information regarding colorectal cancer or skin cancers, including melanoma, leukemia, lymphoma, urinary cancers, and gastric or liver cancer. Of note, while a number of studies reported no increased risk for colon cancer, one study suggested the risk may be as high as thirteen-fold.

Managing Your Endometriosis and Cancer Risk

If you have endometriosis, it’s important to be aware of the potential risks of cancer and take steps to manage your risk. These steps may include regular cancer screening, maintaining a healthy lifestyle, and talking to your doctor about any concerns. In some cases, you may have a genetically founded increased risk. If cancer and/or endometriosis runs in the family, it may be best to consult with an expert. If you are older and have endometriosis, it may also be best to seek expert consultation. It’s important to be aware and proactive, but it’s also important to remember that while the risk may be increased, most women with endometriosis will not develop cancer.

Endometriosis and Cancer: A Systematic Review and Meta-Analysis

Marina Kvaskoff, Yahya Mahamat-Saleh, Leslie V Farland, Nina Shigesi, Kathryn L Terry, Holly R Harris, Horace Roman, Christian M Becker, Sawsan As-Sanie, Krina T Zondervan and more.

Human Reproduction Update, Volume 27, Issue 2, March-April 2021, Pages 393–420,