ERBB2 and breast cancer: However, patients with either high t-erbB2 expression or high t-erbB2s to p185HER2 protein ratio can benefit from tyrosine kinase inhibitor treatments (i.e., lapatinib), without conferring trastuzumab resistance.17,18,33 Inclusion of t-erbB2s into HER2 classification schemes and a more comprehensive understanding of the mechanism(s) of t-erbB2s generation could provide insight into breast cancer pathogenesis, HER2-positive breast patient classification, and treatment considerations.