Our findings demonstrate, however, that some of the genes amplified only in the HER2-negative components of HER2 heterogeneous breast cancers, such as genes previously described as oncogenic, including MDM4 [32], FGFR1 [40,46], ZNF703 [33], MYC, FAM83A [34], RAB11FIP1 [28,29], and PIK3CA (Table 1), as well as BRF2 and DSN1, which were shown to have oncogenic properties here, may constitute potential drivers and compensate for the lack of HER2 amplification. The gene discussed is ERBB2; the disease is breast cancer.