ERBB2 and breast cancer: Somatic mutations in this gene are very rare in the sporadic form, while decreased expression levels of BRCA1 have been identified in the triple negative group, or basal-like subtype, of sporadic breast cancers (ER, PR and HER2 negative) that have genetic profiles similar to BRCA1 mutation carrier tumors [44] and express high levels of ID4 [45].