SMPD1 and cancer: The malignant phenotype of melanoma, in terms of tumour progression and metastatic capacity, is also regulated by sphingolipids [24,25], in particular those originating from the activity of the lysosomal hydrolase acid sphingomyelinase (A-SMase), an enzyme responsible for the conversion of sphingomyelin to ceramide, a well-known pro-apoptotic molecule in both normal and cancer cells [26].