SLC46A3 and breast cancer: SLC46A3 expression, which is high in breast cancer cell lines but varies between other tumour types, might, therefore, be a predictor of T-DM1 sensitivity and has been proposed as a potential patient selection biomarker, with patients or cancer types (e.g. multiple myeloma) that express low levels of SLC46A3, and therefore potentially less sensitive to T-DM1, being more suited to alternative payloads that do not require SLC46A3-mediated transport.57