Upon production, S1P interacts with a family of G protein-coupled receptors (S1PR1–5) on the cell surface [5] and/or intracellular targets, such as histone deacetylase (HDAC) [6] and TRAF2 [7], to play a plethora of roles in diverse pathophysiological conditions such as inflammation, immunity and cancer. Here, HDAC9 is linked to cancer.