Abstract

Previous studies of oral contraceptives (OC) and breast cancer indicate that recent use slightly increases risk, but most studies relied on self-reported use and did not examine contemporary OC formulations. This nested case-control study was among female enrollees in a large US integrated health care delivery system. Cases were 1,102 women ages 20–49 diagnosed with invasive breast cancer from 1990–2009. Controls were randomly sampled from enrollment records (n=21,952) and matched to cases on age, year, enrollment length, and medical chart availability. Detailed OC use information was ascertained from electronic pharmacy records and analyzed using conditional logistic regression, odds ratios (OR), and 95% confidence intervals (CI). Recent OC use (within the prior year) was associated with an increased breast cancer risk (OR=1.5, 95% CI=1.3–1.9) relative to never or former OC use. The association was stronger for ER+ (OR=1.7, 95% CI=1.3–2.1) than ER− disease (OR=1.2, 95% CI=0.8–1.8), though not statistically significantly different (p=0.15). Recent use of OCs involving high dose estrogen (OR=2.7, 95% CI=1.1–6.2), ethynodiol diacetate (OR=2.6, 95% CI=1.4–4.7), or triphasic dosing with an average of 0.75 milligrams of norethindrone (OR=3.1, 95% CI=1.9–5.1, p for heterogeneity compared to using other OCs=0.004) was associated with particularly elevated risks, while other types including low dose estrogen OCs were not (OR=1.0, 95% CI=0.6–1.7). Our results suggest that recent use of contemporary OCs is associated with an increased breast cancer risk, which may vary by formulation. If confirmed, consideration of the breast cancer risk associated with different OC types could impact discussions weighing recognized health benefits and potential risks.

Abstract Source: https://www.ncbi.nlm.nih.gov/pubmed/25085875

Recent oral contraceptive use by formulation and breast cancer risk among women 20 to 49 years of age.
Beaber EF, Buist DS, Barlow WE, Malone KE, Reed SD, Li CI.
Cancer Res. 2014 Aug 1;74(15):4078-89. doi: 10.1158/0008-5472.CAN-13-3400.
PMID: 25085875