PDGFRB and breast cancer: Six fibroblast markers (Costa et al., 2018) [fibroblast activation protein (FAP), integrin b1 (ITGB1), a-smooth muscle actin (aSMA), fibroblast-specific protein-1 (FSP-1), platelet-derived growth factor receptor b (PDGFRB), and caveolin-1 (CAV1)] have been used to delineate CAFs subtypes which were linked to immunosuppression and resistance to immunotherapy in breast cancer (Kieffer et al., 2020).