The association between oral contraceptive use and lobular and ductal breast cancer in young women.

Recent reports indicate that the incidence of lobular breast cancer is increasing at a faster rate than ductal breast cancer, which may be due to the differential effects of exogenous hormones by histology. To address this issue, we examined whether the relationship between oral contraceptive use and incident breast cancer differs between lobular and ductal subtypes in young women. A population-based sample of in situ and invasive breast cancer cases between ages 20 and 44 were recruited from Atlanta, GA; Seattle-Puget Sound, WA and central New Jersey. Controls were sampled from the same areas by random-digit dialing, and were frequency matched to the expected case age distribution. Odds ratios (ORs) and 95% confidence intervals (95% CIs) were calculated using polytomous logistic regression. Among the 100 lobular cancers, 1,164 ductal cancers, and 1,501 controls, the odds ratios for oral contraceptive ever use were 1.10 (95% CI = 0.68-1.78) for lobular cancers and 1.21 (95% CI = 1.01-1.45) for ductal cancers, adjusted for study site, age at diagnosis, and pap screening history. Our results suggest that the magnitude of the association between ever use of oral contraceptives and breast cancer in young women does not vary strongly by histologic subtype. These results are similar to previous studies that report little difference in the effect of oral contraceptive use on breast cancer by histology.