S1PR1 and cancer: Systemic S1P has been shown to mediate cell-cell communication between host cells and cancer cells to promote various aspects of metastasis of tumor, including S1P secretion from lymphoid endothelial cells and S1PR1-dependent or S1PR2-dependent signaling in cancer cells to induce migration and/or evade immune-cell-mediated cytotoxicity (Mao et al., 2010; Ponnusamy et al., 2012; van der Weyden et al., 2017; Ogretmen, 2018).