SPHK1 and colonic neoplasm: Growth-inhibitory effects elicited by SphK1 inhibition in colon cancer cells depend upon p53 functional activity since reduction of colon cancer cell growth and induction of apoptosis induced by SphK1 inhibition by specific inhibitor SK1-I is more enhanced in wild-type p53 cells than in cells with inactivated or mutated p53 [66].