Type and risk of cancer related to endometriosis: ovarian cancer and beyond

Endometriosis is a common disease in reproductive age women with an incidence of about 10% depending on the definition and cohort characteristics. The pathological diagnosis is a benign, but the disease often recurs and can in rare cases metastasise like a cancer. Endometriosis poses unique surgical challenges and can result in surgical procedures that are more technically difficult than those for malignant disease. Saraswat et al. analysed outcomes of 17 834 women with surgically diagnosed endometriosis and found a hazard ratio of 1.7 for ovarian cancer. The current Scottish nationwide study did not specify the histologic type of ovarian cancer. Endometriosis has been associated with increased risk of several subtypes of epithelial ovarian cancer: low-grade serous, clear cell and endometrioid (Pearce, Lancet Oncol 2012;13:385–94). Aside from ovarian cancer, the risk of several types of cancer, including breast cancer, haematologic malignancies, non-Hodgkin's lymphoma and brain tumours, is increased in patients with endometriosis (Melin et al. Human Reprod. 2006;21:1237–42; Brinton et al. Obstet Gynecol 1997;176:572–9). In the current study, the risk of these cancers was not increased, but that may have been due to the relatively small sample size. In both clinical and research settings, there are several issues to be addressed. First, information regarding the true incidence of endometriosis is lacking and may be underestimated. A laparoscopic biopsy is necessary to confirm the diagnosis and many women may remain asymptomatic or never present for surgical management. Secondly, we do not have enough information to identify which subgroups of women with endometriosis are at risk for endometriosis-related malignant disease. Endometriosis-associated endometrioid ovarian cancer shares symptoms with endometriosis, including dysmenorrhoea (28.0%), dyspareunia (20.7%) and infertility (14.6%) (Lim et al. Cancer Epidemiol Biomarker Prev 2010;19:398–404). These symptoms have also been reported in endometriosis-related ovarian clear cell carcinoma [dysmenorrhoea (31.3%), dyspareunia (37.5%) and infertility (31.3%)] and are newly developed or exacerbated by the presentation of ovarian cancer (Lim et al. Gynecol Endocrinol 2009;25:435–40). The retrospective study design prevents a clear delineation of when symptoms began. Acute or subacute exacerbation of symptoms might suggest endometriosis-related ovarian cancer but should be considered in conjunction with imaging and serum CA125 and HE4 (Zapardiel et al. Int J Gynecol Cancer 2016;26:52–5). Thirdly, the aetiology of cancer in women with endometriosis is not clear: it may result from a shared aetiology or as a secondary effect of endometriosis. A better understanding of the underlying aetiology may allow tailored interventions to prevent endometriosis-related malignant disease. Fourthly, the effect of surgical treatment and long-term use of conservative medical treatment on the endometriosis-related malignancy has not been clearly established. Women with endometriosis have a higher risk of low-grade serous, clear cell and endometrioid ovarian cancer. New development or exacerbation of existing endometriosis-related symptoms such as dysmenorrhoea, dyspareunia and infertility should raise a red flag for the possibility of endometriosis-related ovarian cancer, especially in the presence of an accompanying solid mass and elevated serum HE4. None declared. Completed disclosure of interests form available to view online as supporting information. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.