Oral Contraceptives and Breast Cancer Risk Overall and by Molecular Subtype Among Young Women

Background: Evidence suggests that recent oral contraceptive (OC) use is associated with a small increased breast cancer risk; yet risks associated with contemporary OC preparations and by molecular subtype are not well characterized. Methods: We conducted a population-based case–control study of invasive breast cancer among women ages 20 to 44 residing in the Seattle–Puget Sound area from 2004 to 2010 (985 cases and 882 controls). We collected information on contraceptive use and participant characteristics via an in-person interview. Multivariable-adjusted logistic regression was used to calculate odds ratios (OR) and 95% confidence intervals (CI). Results: Lifetime duration of OC use for ≥15 years was associated with an increased breast cancer risk (OR, 1.5; 95% CI, 1.1–2.2). Current OC use (within 1 year of reference date) for ≥5 years was associated with an increased risk (OR, 1.6; 95% CI, 1.1–2.5) and there were no statistically significant differences in risk by OC preparation. Risk magnitudes were generally greater among women ages 20 to 39, and for estrogen receptor–negative (ER−) and triple-negative breast cancer (current use for ≥5 years among ages 20–39: ER− OR, 3.5; 95% CI, 1.3–9.0; triple-negative OR, 3.7; 95% CI, 1.2–11.8), although differences between groups were not statistically significant. Conclusions: Long-term use of contemporary OCs and current use for ≥5 years was associated with an increased breast cancer risk among women ages 20 to 44. Risk may be greater among younger women and for ER− and triple-negative breast cancer, but these findings require confirmation. Impact: Continued surveillance and pooled analyses of OC use and breast cancer risk by molecular subtype are needed as OC preparations evolve. Cancer Epidemiol Biomarkers Prev; 23(5); 1–10. ©2014 AACR .