ERBB2 and breast cancer: In addition to the trend of HER2 overexpression and amplification, in our subset of tumors, we found co-amplification and polysomy (3/112; 3%) and a subgroup of tumors negative to immunohistochemistry but positive to HER2 gene amplification (3/8; 37.5%); this lack of concordance between immunohistochemistry and ISH has recently been described in human breast cancer [50].