Two independent studies reported loss of SLC46A3 expression in T-DM1-resistant BT-474 and NCI-N87 cells, in which sensitivity to the agent could be restored by forced expression of SLC46A3, and in a T-DM1-resistant HER2-positive invasive ductal carcinoma patient-derived xenograft model.29,57 Functionally, knockdown of SLC46A3 in BT-474 or knockout in SK-BR-3 cells markedly reduced sensitivity to T-DM1. This evidence concerns the gene SLC46A3 and invasive ductal breast carcinoma.