Use of oral contraceptives and endometrial cancer risk (Sweden)

Objectives: To estimate the magnitude and persistence of the protective eff ect of use of combined oral contraceptives (COCs) and endometrial cancer ri sk. Methods: We performed a nation-wide, population-based case-control study am ong postmenopausal women aged 50-74 years in Sweden, which included 709 sub jects with incident, histopathologically verified endometrial cancer, and 3 ,368 controls with an intact uterus. We used unconditional logistic regress ion to calculate odds ratios as estimates of relative risks. Results: Use of any sort of oral contraceptive decreased risk for endometri al cancer by 30%, while progestin-only pills reduced risk more markedly. Fo r COCs the reduction in risk was noticeable following 3 or more years of us e (OR 0.5, 95% CI 0.3-0.7), and increased with duration of intake, reaching 80% lower risk after 10 years of use. The protective effect of COC use was similar for all degrees of tumor differentiation and invasiveness, and rem ained for at least 20 years after cessation of use. Subsequent use of hormo ne replacement did not modify these protective effects. Conclusions: We conclude that COC use confers a long-lasting protection aga inst endometrial cancer risk which is particularly marked for long-term use rs.