Hormonal and surgical treatments for endometriosis and risk of epithelial ovarian cancer

Objective. Whether hormonal or surgical treatment of endometriosis is associated with risk of epithelial ovarian cancer. Design. Nested case-control study. Setting. Sweden. Population. All women with a first-time discharge diagnosis of endometriosis in 1969-2007 were identified using the National Swedish Patient Register and constituted our study base. Methods. By linkage to the National Swedish Cancer Register we identified all women diagnosed with epithelial ovarian cancer at least one year after the endometriosis diagnosis (cases). Two controls per case with no ovarian cancer before the date of cancer diagnosis of the case were randomly selected from the study base and matched for year of birth. Two-hundred-and-twenty cases and 416 controls entered the study. Information on hormonal and surgical treatments and other reproductive factors was extracted from medical records according to pre-specified protocols. Conditional logistic regression was used for all calculations. Main outcome measures. Crude and adjusted odds ratios (OR) with 95% confidence intervals (CI) for all hormonal as well as surgical treatments. Results. There was a significant association between one-sided oophorectomy, as well as for radical extirpation of all visible endometriosis, and ovarian cancer risk in both univariate analyses (crude OR 0.42, 95% CI 0.28-0.62 and OR 0.37, 95% CI 0.25-0.55, respectively) and multivariate analyses (adjusted OR 0.19, 95% CI 0.08-0.46 and OR 0.30, 95% CI 0.12-0.74, respectively). Conclusions. One-sided oophorectomy as well as radical extirpation of all visible endometriosis is protective against later development of ovarian cancer.