S1PR1 and myeloid sarcoma: FTY720 is a prodrug approved as a medicine for MS patients that must be phosphorylated to become an active agent (FTY720-P), where it acts a structural analog of sphingosine 1-phosphate (S1P; Blaho and Hla, 2014) to target S1P1,3,4,5 (Brinkmann et al., 2002; Mandala et al., 2002).