BACKGROUND: The etiology of breast cancer and our understanding on the carcinogenicity of different risk factors is impotant for control programms.
OBJECTIVE: We investigated the expression of estrogen and progesterone receptors (ER, PR), and human epithelial receptor 2 (HER2) overexpression and its associations, with environmental risk factors among breast cancer patients.
METHODS: We classified the patients into four groups including; triple negative (ER–/PR–/HER2-), HER2-overexpression (ER–/PR–/HER2+), luminal A (ER+ and/or PR+/HER2-) and luminal B (ER+ and/or PR+/HER2+). We used a case-only design and multinomial logistic regression analyses.
RESULTS: In premenopausal patients, those with high BMI had lower prevalence of luminal B tumors compared to luminal A groups (OR= 0.42, 95% CI= 0.23 to 0.74). However, in the postmenopausal groups, prevalence of the luminal B tumors was less than luminal A tumors oral contraceptive pill (OCP) users (OR= 0.64, 95% CI= 0.42 to 0.98). In addition, among those who had an older age at menarche had a higher risk of ER2-overexpression tumors compared to luminal A tumors (OR= 2.82, 95% CI= 1.29-6.19).
CONCLUSIONS: Expression of HER2, ER, and PR, among breast cancer patients seems to be associated with OCP use, BMI, age at menarche and age at first pregnancy.