ERBB3 and breast cancer: Recent evidence indicates that in ERBB2 non-amplified breast cancer, somatic mutation of ERBB2 (ERBB2mut) and/or ERBB3 (ERBB3mut) may provide an alternative mechanism for upregulation of HER2 activity that is therapeutically tractable using second generation HER2 tyrosine kinase inhibitors such as neratinib [13, 14].