Differentially Expressed MicroRNAs in Postpartum Breast Cancer in Hispanic Women

National Cancer Institute [3U01CA153086-01, 3U01CA153086-02S1

Reproductive Factors, Heterogeneity, and Breast Tumor Subtypes in Women of Mexican Descent

NIH/NCI grants [UO1CA153086, CA023074-2953, CA116199-02S1]; Avon Foundation; Susan G. Komen for the Cure [KG090934

Hypothesized role of pregnancy hormones on HER2+ breast tumor development

Breast cancer incidence rates have declined among older but not younger women; the latter are more likely to be diagnosed with breast cancers carrying a poor prognosis. Epidemiological evidence supports an increase in breast cancer incidence following pregnancy with risk elevated as much as 10 years postpartum. We investigated the association between years since last full-term pregnancy at the time of diagnosis (≤10 or >10 years) and breast tumor subtype in a case series of premenopausal Hispanic women (n = 627). Participants were recruited in the United States, Mexico, and Spain. Cases with known estrogen receptor (ER), progesterone receptor (PR), and HER2 status, with one or more full-term pregnancies ≥1 year prior to diagnosis were eligible for this analysis. Cases were classified into three tumor subtypes according to hormone receptor (HR+ = ER+ and/or PR+; HR− = ER− and PR−) expression and HER2 status: HR+/HER2−, HER2+ (regardless of HR), and triple negative breast cancer (TNBC). Case-only odds ratios (ORs) and 95% confidence intervals (CIs) were calculated for HER2+ tumors in reference to HR+/HER2− tumors. Participants were pooled in a mixed-effects logistic regression model with years since pregnancy as a fixed effect and study site as a random effect. When compared to HR+/HER2− cases, women with HER2+ tumors were more likely be diagnosed in the postpartum period of ≤10 years (OR=1.68; 95% CI, 1.12–2.52). The effect was present across all source populations and independent of the HR status of the HER2+ tumor. Adjusting for age at diagnosis (≤45 or >45 years) did not materially alter our results (OR=1.78; 95% CI, 1.08–2.93). These findings support the novel hypothesis that factors associated with the postpartum breast, possibly hormonal, are involved in the development of HER2+ tumors