SPNS2 and cancer: S1P can be secreted from cancer cells via specific transporters like protein spinster homolog 2 (SPNS2) and ABC transporters, of which the latter involve ABC sub-family A member 1 (ABCA1), ABC sub-family C member 1 (ABCC1), and ABC sub-family G member 2 (ABCG2) (Geffken and Spiegel, 2018).