Women with endometriosis incur a twofold to threefold higher risk of developing one of three particular subtypes of ovarian cancers compared with women who do not have endometriosis, a large study has revealed.

A common gynecologic disorder affecting about 10% of women of reproductive age, endometriosis has been associated with a risk for developing epithelial ovarian cancer, the most prevalent and deadly form of the disease. But according to a statement issued by The Lancet Oncology, in which the study findings were reported, these results definitively confirm the magnitude of this risk and the relationship with specific subtypes, and could lead to better identification and, possibly, increased surveillance of women at heightened risk for ovarian cancer.

The Ovarian Cancer Association Consortium analyzed data from 13 case-control studies of ovarian cancer. Of the 13,226 controls and 7,911 women with invasive ovarian cancer, 818 and 738, respectively, reported a history of endometriosis. Also included in the analysis were 1,907 women with borderline ovarian cancer, 168 of whom reported a history of endometriosis.

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The researchers found that self-reported endometriosis was associated with a significantly increased risk of three subtypes of ovarian cancer:

  • Clear-cell—136 (20.2%) of 674 cases vs 818 (6.2%) of 13,226 controls (odds ratio [OR] 3.05)
  • Low-grade serous—31 (9.2%) of 336 cases (OR 2.11)
  • Endometrioid invasive—169 (13.9%) of 1,220 cases (OR 2.04).

These results represent the first time endometriosis has been linked with low-grade serous ovarian cancers; women with a history of endometriosis have more than double the risk of developing this cancer subtype.

No association was found between endometriosis and high-grade serous, mucinous, serous borderline, or mucinous borderline ovarian cancers.