interaction of estrogen and progesterone receptors, and human epithelial receptor 2, with breast cancer risk factors: a multi-center case-only study in iran

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.