Epidemiological evidence suggests that Breast Cancer (BC) risk factors (i.e breastfeeding, parity, menarche, etc.) may vary by tumor pathology. We assessed if BC risk related to urinary monomethyl arsenic acid percentage (%MMA) vary by molecular subtype. A total of 499 patients were assigned to one of three tumor marker categories: HR+ (ER+ and/or PR+ and HER2-), HER+ (regardless of ER or PR status) and TNBC (ER-,PR-, and HER2-). Controls were healthy women, with no history of cancer, matched 1:1 by age.%MMA remained as a significant risk factor for BC only for HR+. HER2+ and TNBC tumors were not significantly associated with urinary arsenic (As) metabolites. Our results suggest that increased BC risk related to As exposure is not mediated by HER2 expression. This is the first report on As exposure and BC molecular subtypes which requires further confirmation.
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