MDA-MB-361 and MDA-MB-453 were selected for screening out of five potential HER2-positive breast cancer that were confirmed to have ERBB2 gene amplification by FISH and HER2 protein expression by Western blotting (Fig. S1), on the basis of sensitivity to T-DM1 and insensitivity to the cell-autonomous effects of trastuzumab, broadly matching the clinical setting in which T-DM1 is used (Fig. S2). This evidence concerns the gene ERBB2 and breast cancer.