S1PR1 and cancer: S1P, whether produced by SphK1 or SphK2, owes almost all of its bioactive pleiotropic effects on cell survival, migration, angiogenesis, and lymphangiogenesis and immune cell recruitment, all processes that may be involved in cancer, to S1PR1–5, which are S1P-specific G protein-coupled receptors (GPCRs) [4, 43].