ERBB2 and neoplasm: Thus the lack of improved outcomes of T-DM1 and T-DM1-P compared with trastuzumab plus chemotherapy in the MARIANNE and KRISTINE studies could be explained partially by lack of effect of T-DM1 on cells that do not overexpress HER2 but coexist with the HER2 overexpressing cells in a heterogeneous tumour [18].