Hysterectomy and risk of epithelial ovarian cancer by histologic type, endometriosis, and menopausal hormone therapy.

ABSTRACT

BACKGROUND: This nationwide, register-based case-control study investigated the association between hysterectomy and risk of epithelial ovarian cancer according to histology and by history of endometriosis and menopausal hormone therapy (MHT) use. METHODS: From the Danish Cancer Registry, all women registered with epithelial ovarian cancer at age 40-79 years during 1998-2016 were identified (n = 6738). Each case was sex- and age-matched to 15 population controls using risk-set sampling. Information on previous hysterectomy on benign indication and potential confounders was retrieved from nationwide registers. Conditional logistic regression was used to calculate odds ratios (ORs) with 95% confidence intervals (CIs) for the association between hysterectomy and ovarian cancer according to histology, endometriosis, and use of MHT. RESULTS: Hysterectomy was not associated with risk of epithelial ovarian cancer overall (OR=0.99; 95% CI 0.91 -1.09) but was associated with reduced risk of clear cell ovarian cancer (OR=0.46; 95% CI 0.28-0.78). In stratified analyses, decreased ORs associated with hysterectomy were seen in women with endometriosis (OR=0.74; 95% CI 0.50-1.10) and in non-users of MHT (OR=0.87; 95% CI 0.76-1.01). In contrast, among long-term MHT users, hysterectomy was associated with increased odds for ovarian cancer (OR=1.20; 95% CI 1.03-1.39). CONCLUSION: Hysterectomy was not associated with epithelial ovarian cancer overall but with reduced risk of clear cell ovarian cancer. Our findings may suggest a reduced risk of ovarian cancer after hysterectomy in women with endometriosis and in MHT non-users. Interestingly our data pointed to an increased ovarian cancer risk associated with hysterectomy among long-term users of MHT.