Prospective cohort study of the association of bilateral oophorectomy and the risk of colorectal cancer

Worldwide, colorectal cancer is the second most common cancer in women. Estrogen exposure has been inversely associated with colorectal cancer. A prospective cohort study in Denmark (25.698 female nurses; aged ≥ 45 years; 542,140 person-years of follow-up) found that bilateral oophorectomy was associated with a 79% increased risk of colorectal cancer (aRR 1.79; 95% CI 1,33-2,42). Unilateral oophorectomy was associated with a statistically non-significant increased risk (aRR 1.25; 95% CI 0.86-1.82). The associations were not modified by baseline HRT use, menopausal status, hysterectomy, or BMI.