In light of the importance of ERBB2 in breast cancer, HB4a [16] and HB4aC5.2 [17], the parental and the ERBB2 overexpressing cell lines, respectively, have been used to investigate quantitative transcriptional alterations in mammary cells mediated by ERBB2 overexpression [18], [19]. This evidence concerns the gene ERBB2 and breast carcinoma.