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. (C) 2014 AACR.