Ovarian cancer risk in women with endometriosis

22 February 2012

A study published today in Lancet Oncology suggests that women with endometriosis are associated with a higher risk of developing three specific types of ovarian cancer.
However, the World Endometriosis Society (WES) explains that the overall risk factor for women with endometriosis to develop ovarian cancer continues to remain low.

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, across North America, Australia, and Europe, which included data from over 23,000 women (13,326 controls, 7,911 with invasive ovarian cancer, 1,907 with borderline cancer) [1].

The authors found that 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).

World Endometriosis Society explains the real risk

According to the article published today, women with endometriosis have an odds ratio of about 1.5 of developing an invasive ovarian cancer compared to the general female population.

“From this point of view, these data are “reassuring” in comparison with some previous reports indicating a much higher risk. An odds ratio of 1.5 means that a woman with endometriosis has a life-time risk of developing an ovarian cancer of about 1.5% instead of 1%”

WES President, Paolo Vercellini

said World Endometriosis President, Professor Paolo Vercellini.

Whereas the study showed no link between endometriosis and high-grade serous, mucinous, serous borderline, or mucinous borderline ovarian cancers, the authors stress that their paper describes for the first time an association between endometriosis and low-grade serous ovarian cancers translating to a doubling of the risk in women with a history of endometriosis.

Professor Vercellini agrees this is an important finding, but does offer another word of caution:

This finding only has pathogenic and not clinical implications, as the incidence of this cancer subtype is limited to 336 out of 7911 cases in this pooled analysis and thus the practical consequences are modest.

Indeed he stresses that it is important to be cautious with the definition of endometriosis in general as a precursor lesion for clear-cell and endometrioid ovarian cancers, as reasonably only atypical endometriosis should be considered a definite precursor lesion [2].

Furthermore, without the specification of which sub-types of endometriosis, the lack of information on subsequent treatment with or without danazol, and the possible differential recalling rate between cases and controls, there are still some uncertainties that need to be resolved in future studies.

In particular, future studies need to determine whether the association is causal with a clear temporal relationship or merely association due to exposure to shared risk factors.

Protecting against ovarian cancer

This study, in line with previous studies on endometriosis and cancer, shows that most women with endometriosis do not develop ovarian cancer.

However, healthcare providers should be alerted to the increased risk, however slight, of specific subtypes of ovarian cancer in women with a history of endometriosis.

Interestingly the authors have chosen not to mention the protective effect of oral contraceptives, bearing in mind that one of the co-authors is also the co-author of the article by Modugno et al demonstrating the effect of OCs on ovarian cancer risk in women with endometriosis [3].


  1. Pearce CL et al. Association between endometriosis and risk of histological subtypes of ovarian cancer: a pooled analysis of case–control studies. Lancet Oncology 2011.
  2. Wei JJ et al. Endometriosis and ovarian cancer: a review of clinical, pathologic, and molecular aspects. Int J Gynecol Pathol 2011;30:553-68.
  3. Modugno F et al. Oral contraceptive use, reproductive history, and risk of epithelial ovarian cancer in women with and without endometriosis. Am J Obstet Gynecol 2004;191:733-40.