Oral contraceptive use has previously been suggested as a risk factor for breast cancer, and there is some evidence that this association may stronger for estrogen receptor (ER)-negative than ER-positive breast cancer.1 Taken together with the findings of Altundag et al.,2 we agree that oral contraceptive use could plausibly be associated with an increased risk of triple-negative breast cancer. However, the majority of the literature indicates that any association between oral contraceptive use and breast cancer risk is likely restricted to young, premenopausal women.3 Because our study examining risk factors for triple-negative, HER-2-overexpressing, and luminal breast cancers was restricted to women aged ≥55 years,4 we did not expect to observe any associations with oral contraceptive use. In re-examining our data, we found a higher prevalence of ever-use of oral contraceptives in our triple-negative case group (48%) compared with cancer-free controls (38%); however, these differences were not found to be statistically significant, and after accounting for differences in age we observed no association between oral contraceptive use and the risk of triple-negative breast cancer (odds ratio of 0.9). Based on these data, we cannot rule out an association between oral contraceptive use and the risk of triple-negative breast cancer, but we believe that such an association is more likely to be observed in a younger study population. Given that triple-negative breast tumors tend to be diagnosed at an earlier age compared with tumors of the more common luminal subtype, factors associated with an increased risk of early-onset breast cancer, such as oral contraceptive use, may be hypothesized be more strongly associated with the risk of triple-negative disease. As the epidemiologic literature regarding this clinically relevant breast cancer subtype continues to develop, it will be interesting to discover whether risk factors for triple-negative breast cancer differ according to age at diagnosis and menopausal status.
Amanda I. Phipps MPH* , Christopher I. Li MD, PhD* , * Division of Public Health Sciences, Fred Hutchinson Cancer Research Center, Seattle, Washington, Department of Epidemiology, School of Public Health and Community Medicine, University of Washington, Seattle, Washington.