Women with a history of endometriosis are significantly more likely to develop three specific types of ovarian cancer (clear cell, endometrioid, and low-grade serous), according to an article published Online First in the Lancet Oncology.
Although several small studies have suggested that endometriosis (a common gynaecological disorder that affects about 10% of women of reproductive age) is associated with a risk of developing epithelial ovarian cancer (the most deadly and prevalent form), this study definitively confirms the magnitude of this risk and the relationship with specific subtypes.
"This breakthrough 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 individualisation of prevention and early detection approaches such as risk-reduction surgery and screening", explains Celeste Leigh Pearce from the University of Southern California, Los Angeles, USA, lead author of the study.
In this study, a team from The Ovarian Cancer Association Consortium (OCAC) calculated the size of the association between endometriosis and the risk of the five major ovarian cancer histological subtypes separately (high-grade serous, low-grade serous, clear cell, endometrioid, and mucinous carcinomas). The study consisted of a pooled analysis of 13 case-control studies, which included data from over 23 000 women (13 326 controls, 7911 with invasive ovarian cancer, 1907 with borderline cancer).
The researchers estimated that endometriosis is linked to a more than threefold chance of developing clear-cell ovarian cancers, and is associated with more than double the risk of developing endometrioid tumours.
Importantly, for the first time an association between endometriosis and low-grade serous ovarian cancers was noted; translating to a doubling of the risk in women with a history of endometriosis.
No link was found between endometriosis and high-grade serous, mucinous, serous borderline, or mucinous borderline ovarian cancers.
The authors 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, healthcare providers should be alert to the increased risk of specific subtypes of ovarian cancer in women with a history of endometriosis."*
In an accompanying Comment, Charlie Gourley from University of Edinburgh Cancer Research UK Centre, Edinburgh, UK points out: "Although the risk of epithelial ovarian cancer shown by the results is perhaps not in itself sufficient to justify targeted ovarian-cancer screening of patients with a history of endometriosis, the fact that some of the associated histological subtypes (eg, clear-cell) predominantly present at an early stage (allowing possible curative resection) makes this a consideration."
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