Use of oral contraceptives,intrauterine devices and tubal sterilization and cancer risk in a large prospective study,from 1996 to 2006

The association of contraceptive methods, including oral contraceptives (OC), intrauterine devices (IUD) and tubal sterilization (TS), with overall and site‐specific cancer were prospectively investigated in a cohort of 66,661 Chinese women in Shanghai, 76.7% of whom used contraception. During a median follow‐up time of 7.5 years, 2,250 women were diagnosed with cancer. Ever‐use of any contraceptive method was not associated with overall cancer risk adjusted hazard ratio (HR_adj) = 1.02, 95% CI, 0.92–1.12]. Use of any contraceptive method was associated with increased risk of rectal cancer (HR_adj = 1.68, 95% CI, 1.08–2.62) and reduced risk of thyroid cancer (HR_adj = 0.63, 95% CI, 0.38–1.04). Risk of gallbladder cancer increased with ever use of OC (HR_adj = 2.38, 95% CI, 1.26–4.49). IUD use was associated with a possible reduced risk of thyroid cancer (HR_adj = 0.64, 95% CI, 0.38–1.07). Longer duration of IUD use decreased risk for breast, thyroid and lung cancers. Ever having a TS was associated with increased uterine body cancer (HR_adj = 2.50, 95% CI, 1.47–4.25) and decreased risk of stomach cancer (HR_adj = 0.59, 95% CI, 0.39–0.91). We did not find any contraceptive method to be related to the risk of ovarian cancer but the analyses were based on few events. Although chance findings are a likely explanation for some of the associations found in our study, these findings suggest that various contraceptive methods or reproductive patterns may play a role in the etiology of cancer. © 2008 Wiley‐Liss, Inc.