Bilateral Oophorectomy and Colorectal Cancer Incidence and Mortality in the Women's Health Initiative

Background: The few cohort studies examining oophorectomy and colorectal cancer risk provide mixed results. Therefore, we examined this issue in Women's Health Initiative Observational Study participants.Methods: A total of 71,312 postmenopausal women were followed for 22.1 years (median). At enrollment, 55,643 (78%) had intact ovaries and 15,669 (22%) had undergone a bilateral oophorectomy. Colorectal cancers were verified by central medical record review with mortality findings enhanced by National Death Index queries.Results: With 1,421 incident colorectal cancers, 450 colorectal cancer-specific mortalities, after controlling for covariates, bilateral oophorectomy was not associated with colorectal cancer incidence or colorectal cancer mortality.Conclusions: No significant associations between oophorectomy and colorectal cancer incidence and mortality were seen in a large cohort study with long follow-up.Impact: As the oophorectomy and colorectal cancer question remains open, further studies of high quality, even with null findings, should be encouraged.