CYCS and cancer: Therefore, inhibition of Sphk1 will reduce S1P production and increase sphingosine, promoting cancer cells’ death, which has been supported by several in vitro studies; for example, downregulation of Sphk1 by small interfering RNA targeting human Sphk1 has been found to promote apoptosis in many types of cancer cells, including colon, breast, prostate, glioblastoma, and leukemia, and the increased apoptosis triggered by Sphk1 siRNA was associated with the activation of mitochondrial pathway, including the increase of caspases activation and the release of cytochrome C and sphingosine [24].