PDPN and cancer: In this regard, it is worth noting that in autoimmune arthritis, expression of FAP and PDPN marks a subset of synovial fibroblasts that promote autoimmune inflammatory damage (Croft et al., 2019), while FAP+ PDPN+ fibroblasts in the cancer setting may mediate the exclusion of T cells from tumor infiltration, through TGFβ signaling and fibrosis as well as nitric oxide-mediated T cell suppression (Monteran and Erez, 2019).