ERBB2 and breast cancer: Several studies have shown that PABC seems to be more commonly associated with less favorable tumor characteristics, such as a reduced expression of estrogen (ER) and/or progesterone (PR) receptors, and of HER2/neu [27,41,42], although there are studies supporting that there are no significant differences in the expression of hormone receptors and HER2 between PABC and non-pregnancy-associated breast cancer [43].