There has always been concern about whether endometriosis increases a woman’s cancer risk. Now a new study that included nearly 50,000 women offers some reassuring news…but also a serious warning.

The upshot: While the increase in cancer risk overall is limited and low, it all depends on the type of endometriosis you have.

PINPOINTING THE RISK

You already know the basics about endometriosis. Tissue that’s usually found inside the uterus grows outside of it, causing pain for most women with the condition and fertility problems for many. But you may not know that there are three different types of endometriosis based on the location of the growth…

Peritoneal endometriosis: The most common type. Growths develop anywhere in the pelvic cavity.

Deep infiltrating endometriosis: The rarest type. Growths develop within the pelvic cavity but also extend deep into tissues.

Ovarian endometriosis: Just as it sounds, growths develop within the ovaries.

The study. Researchers in Finland analyzed the hospital records of women who had had surgery to treat their endometriosis to look for associations between the three types of the disease and various types of cancers of the reproductive organs.

The good news: None of the types of endometriosis raised the risk for endometrial cancer or other uterine cancers, cervical cancer or genital cancer. Surprisingly, there was a decrease in the risk for squamous cell cervical cancer among women with endometriosis, though it’s unclear why.

Women with peritoneal or deep infiltrating endometriosis did not have a higher overall risk for ovarian cancer than the average woman, though the researchers did say that longer study is needed to better understand whether deep infiltrating endometriosis could have a cancer association over the long-term.

The not-so-good news: Women with ovarian endometriosis had a higher risk for ovarian cancer than the average woman, particularly for two rare types of cancer—clear cell ovarian cancer and endometrioid ovarian cancer. The number of women with ovarian endometriosis who got ovarian cancer was relatively small at 2%, but that risk was higher than earlier studies had found and higher than the 1.3% risk for ovarian cancer among women in general. These women also had a higher-than-usual risk for borderline ovarian tumors, growths that begin along the outer edges of the ovaries, meaningful because these are thought to be starting points for ovarian cancer due to endometriosis.

WHAT THIS MEANS FOR YOU

The study authors said that even though the absolute risk for ovarian cancer remained relatively small, knowing about this risk could help women make decisions about treatment of ovarian endometriosis—in particular, whether to opt for ovarian conservation (keeping the ovaries) vs. removing the ovaries. (Once the ovaries are removed, the risk for ovarian cancer drops substantially.)

Bottom line: Each woman with endometriosis should talk with her doctor about the type she has…any resulting effect on her risk for ovarian cancer…and her treatment options based on this risk. Also consider getting a second opinion from an oncologist who specializes in gynecologic cancers to make the most informed decision.