SPP1 and neoplasm: Taken together, Fan et al., 2018 [33], suggested that OPN-induced EndMT ECs exert CAF-like functions such as promoting tumor growth and metastasis, and Fan et al., 2019 [38], went further to explicitly describe these OPN-EndMT ECs as EndMT-derived CAFs, demonstrating tumor-promoting and immune-modulatory roles.