Patient derived xenografts (PDXs), established by direct transplantation of fresh patient tumor tissue into immunodeficient animals, retain the main histological and genetic characteristics of the patient tumor, and recapitulate its complex interactions with the TME. PDX molecular characterization and correlation with therapeutic response may facilitate biomarker discovery, as well as the identification of primary (and acquired) resistance mechanisms. Drug combinations to be tested in PDX models will be suggested from molecular characterization of patient tumor, responses obtained in patient-derived explant cultures (PDEC), from in silico predictions or from drug screens in breast cancer cell lines. Studies in PDX mice can lead to new hypotheses and support the initiation of new clinical trials.
