FAP and neoplasm: To target tumor-supporting immunosuppressive stroma, many investigations have focused on fibroblast activation protein-α (FAP), a membrane bound serine protease overexpressed by CAFs.28 While both LRRC15 and FAP have been shown to be upregulated by TGFβ,29 recent studies revealed a unique subset of TGFβ-driven CAFs that express LRRC15,4,8 and that these LRRC15+ CAFs are associated with CD8 + T-cell exclusion.8 Our therapeutic studies, a notable observation emerged: LRRC15+ tumors exhibited a concurrent reduction in both growth and the TGFβ–LRRC15 gene signature upon exposure to RIT.