Several small studies have suggested that endometriosis—which affects about 10% of women of reproductive age—is a risk factor for epithelial ovarian cancer. Now, a study published online in Lancet Oncology provides definitive evidence of this link and highlights the risk of specific subtypes of ovarian cancer.1
In the study, a team from the Ovarian Cancer Association Consortium calculated the size of the association between endometriosis and each of the five major ovarian cancer histologic subtypes:
- high-grade serous (odds ratio [OR], 1.13; 95% confidence interval [CI], 0.97–1.32; P = .13)
- low-grade serous (OR, 2.11; 95% CI, 1.39–3.20; P < .0001)
- clear-cell (OR, 3.05; 95% CI, 2.43–3.84; P < .0001)
- endometrioid (OR, 2.04; 95% CI, 1.67–2.48; P < .0001)
- mucinous carcinomas (OR, 1.02; 95% CI, 0.69–1.50; P = .93).
The study consisted of a pooled analysis of 13 case-control studies, which included data from more than 23,000 women (13,326 controls; 7,911 women who had invasive ovarian cancer; and 1,907 women who had borderline cancer).
A history of endometriosis more than tripled the risk of clear-cell ovarian cancer and more than doubled the risk of endometrioid tumors. It also doubled the risk of low-grade serous ovarian cancers.
A link was not found between endometriosis and high-grade serous, mucinous, serous borderline, or mucinous borderline ovarian cancers.
The authors of the published report of the study characterize their findings as a “breakthrough” that “could lead to better identification of women at increased risk of ovarian cancer and could provide a basis for increased cancer surveillance of the relevant population, allowing better individualization of prevention and early detection approaches such as risk-reduction surgery and screening,” according to Celeste Leigh Pearce from the University of Southern California, Los Angeles, the lead author.
But the authors were quick to offer a caution: “Although we have reported strong associations between endometriosis and risk of clear-cell, endometrioid, and low-grade serous ovarian cancers, most women with endometriosis do not develop ovarian cancer. However, health-care providers should be alert to the increased risk of specific subtypes of ovarian cancer in women with a history of endometriosis.”
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