Data from a pooled analysis published in the journal The Lancet Oncology has linked endometriosis with an increased risk of a diagnosis with low-grade serious, endometrioid or clear-cell ovarian cancers.

Endometriosis is a common gynaecological disorder that is characterised by ectopic growth of endometrial glands and stroma. The estimated prevalence in the general population, based on women undergoing tubal ligation, is about 4%; however, the disease is much more common in women with pelvic pain or infertility. Results from previous epidemiological studies have shown conflicting data as to whether there may be an association between endometriosis and epithelial ovarian cancer.

To estimate the consistency and magnitude of the association between endometriosis and risk of the five major histological subtypes of invasive epithelial ovarian cancer and borderline tumours with greater statistical power, the team of researchers conducted a pooled analysis which included data from 13 ovarian cancer case–control studies, part of the Ovarian Cancer Association Consortium, a project founded in 2005 to foster collaborative efforts to discover and validate associations between genetic polymorphisms and risk of ovarian cancer.

A total of 13 226 controls and 7911 women with invasive ovarian cancer were included in this analysis. Of these, 818 and 738, respectively, reported a history of endometriosis. A total of 1907 women with borderline ovarian cancer were also included in the analysis, and 168 of them reported a history of endometriosis.

Self-reported endometriosis was associated with a significantly increased risk of clear-cell, low-grade serous, and endometrioid invasive ovarian cancers. The researchers found no association between endometriosis and risk of mucinous or high-grade serous invasive ovarian cancer, or borderline tumours of either subtype and mucinous.

“Future research should focus on identification of factors that are associated with malignant transformation of endometriosis and subsequent risk of low-grade serous, clear-cell, and endometrioid ovarian cancers to identify women for whom more definitive endometriosis treatment and ovarian cancer surveillance would be appropriate,” the researchers wrote in a news release.