Reproductive factors, heterogeneity, and breast tumor subtypes in women of mexican descent.

Background: Published data support the presence of etiologic heterogeneity by breast tumor subtype, but few studies have assessed this in Hispanic populations.

Methods: We assessed tumor subtype prevalence and associations between reproductive factors and tumor subtypes in 1,041 women of Mexican descent enrolled in a case-only, binational breast cancer study. Multinomial logistic regression comparing HER2(+) tumors and triple-negative breast cancer (TNBC) to luminal A tumors was conducted.

Results: Compared with women with luminal A tumors, those with a later age at first pregnancy were less likely to have TNBC [OR, 0.61; 95% confidence interval (CI), 0.39-0.95], whereas those with three or more full-term pregnancies were more likely to have TNBC (OR, 1.68; 95% CI, 1.10-2.55). A lower odds of TNBC was shown for longer menstruation duration, whether before first pregnancy (OR, 0.78; 95% CI, 0.65-0.93 per 10 years) or menopause (OR, 0.79; 95% CI, 0.69-0.91 per 10 years). Patients who reported breastfeeding for more than 12 months were over twice as likely to have TNBC than luminal A tumors (OR, 2.14; 95% CI, 1.24-3.68). Associations comparing HER2(+) with luminal A tumors were weak or nonexistent except for the interval between last full-term pregnancy and breast cancer diagnosis.

Conclusions: Findings show etiologic heterogeneity by tumor subtype in a population of Hispanic women with unique reproductive profiles.

Impact: Identification of etiologically distinct breast tumor subtypes can further improve our understanding of the disease and help provide personalized prevention and treatment regimens.