PDGFRB and breast cancer: Again, BM-MSCs were not the main contributors to the population of CAFs, as the majority of the PDGFRβ+ and PDGFRβ− CAFs, in the resulting mammary tumors were tdTomato-positive (Supplementary Fig. 5D–F) and therefore derived from the host rather than the transplanted BM (Supplementary Fig. 5G).