ERBB2 and breast carcinoma: While RAC1 has not been shown to be involved in EMT in response to cetuximab treatment and colorectal cancer, studies in breast cancer have shown that RAC1 contributes to resistance to the HER2 inhibitor trastuzumab, and this resistance is associated with alterations in cell morphology that impair trastuzumab-mediated endocytic downregulation of HER2 driven by RAC1 [148].