Oral contraceptive use and other risk factors in relation to HER-2/neu overexpression in breast cancer among young women

This study was undertaken to explore whether the incidence of breast tumors that overexpress HER-2/neu protein product (HER-2/neu+) is more strongly a ssociated with oral contraceptives (OCs) and other factors than is the inci dence of tumors that do not (HER-2/neu-), In a population-based sample of w omen <45 years, 42.9% (159 of 371) of in situ and invasive breast cancer ca ses were HER-2/neu+ as assessed by immunohistochemistry in archived tissue, Polytomous logistic regression was used to calculate the odds ratios (ORs) and 95% confidence intervals (CIs) for HER-2/neu+ and HER-2/neu- breast ca ncer, as compared with 462 population-based controls, in relation to OCs an d other factors. The ratio of the ORs (HER-2/neu+ versus HER-2/neu- tumors) was used as an indicator of heterogeneity in risk, There was little hetero geneity in risk for OC use of 6 months or more by HER-2/neu status (age-adj usted ratio of ORs, 1.29; 95% CI, 0.83-2.00). Among early pill users (less than or equal to 18 years of age) heterogeneity was apparent (2.39; 95% CI, 1.08-5.30), which was attenuated in a multivariate model (1.99; 95% CI, 0. 87-4.54); among cases with estrogen receptor-negative tumors, heterogeneity increased to 5-fold. For other risk factors, there was no marked heterogen eity between + and - tumors for HER-2/neu, In summary, the incidence of bre ast cancer among younger women in relation to OC use at an early age varied with HER-2/neu status, with the odds ratio for + tumors twice that for - t umors.