ERBB2 and breast cancer: In particular, the d16HER2-SRC axis, which amplifies d16HER2-driven oncogenic signals, is active in mammary adenocarcinomas that are transgenic for the human d16HER2 isoform [25,37], genetically engineered cell line models [24], and HER2-positive BC cases [25], confirming that activated SRC is the key surrogate marker that lies downstream of the oncogenic signalling of d16HER2.