SPHK1 and head and neck cancer: When conversion to S1P is blocked by inhibiting SK1, these head and neck cancer cells detoxified sphingosine by converting it to ceramide (Schnute et al, 2012) (Fig. 5C) which is readily transformed into other sphingolipids that lack growth suppressive effects (Spassieva et al, 2007; Hannun and Obeid, 2018).