Previous studies of oral contraceptives and breast cancer have indicated that recent use slightly increases risk, but most studies relied on self-reported use and did not examine contemporary oral contraceptive formulations.
This nested case–control study was among female enrollees in a large U.S. integrated health care delivery system. Cases were 1,102 women ages 20 to 49 years diagnosed with invasive breast cancer from 1990 to 2009.
Controls were randomly sampled from enrollment records ( n = 21,952 ) and matched to cases on age, year, enrollment length, and medical chart availability.
Recent oral contraceptive use ( within the prior year ) was associated with an increased breast cancer risk ( odds ratio, OR=1.5; 95% CI, 1.3–1.9 ) relative to never or former oral contraceptives use.
The association was stronger for estrogen receptor-positive ( ER+; OR=1.7; 95% CI, 1.3–2.1 ) than estrogen receptor–negative ( ER− ) disease ( OR=1.2, 95% CI, 0.8–1.8 ), although not statistically significantly different ( P = 0.15 ).
Recent use of oral contraceptives 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 mg of Norethindrone ( OR,=3.1; 95% CI, 1.9–5.1; P heterogeneity compared with using other oral contraceptives = 0.004 ) was associated with particularly elevated risks, whereas other types, including low-dose estrogen oral contraceptives, were not (OR, 1.0; 95% CI, 0.6–1.7). Our results suggest that recent use of contemporary oral contraceptives was associated with an increased breast cancer risk, which may vary by formulation.
If confirmed, consideration of the breast cancer risk associated with different oral contraceptive types could impact discussions weighing recognized health benefits and potential risks. ( Xagena )
Beaber EF et al, Cancer Res 2014;74;4078–4089