Oral Contraceptive Use and Risks of Cancer in the NIH-AARP Diet and Health Study

Abstract

Although use of oral contraceptives (OC) is common, their influence on carcinogenesis is not fully understood. We used Cox proportional hazards models to examine OC use (never/<1 year (reference), 1–4, 5–9, 10+ years) and development of incident cancers across body sites within the same base population: women in the prospective NIH-AARP Diet and Health Study (enrolled 1995–1996, followed until 2011). Adjustment for confounding varied by outcome; all models accounted for age, race, body mass index, and smoking status and included ≥100,000 women. Any OC use conferred a 3% reduction in the risk for any cancer (hazard ratio = 0.97, 95% confidence interval: 0.95, 0.99). Expected risk reductions that strengthened with duration of use were identified for ovarian and endometrial cancers and were suggested for kidney cancer (P-trends < 0.05). We noted reduced risk for non-Hodgkin lymphoma (hazard ratio = 0.79, confidence interval: 0.64, 0.97) with 10+ years of use. We observed a 37% reduced risk for bladder cancer and 46% increased risk for pancreatic cancer among long-term users who were ≤60 at baseline. OC use did not influence risks for most other cancers evaluated. Given the high prevalence of use and changing formulations, future studies are warranted to fully understand the chemopreventive effects of these medications.