SMPD1 and neoplasm: The extracellular mis-localization of lysosomal cathepsins stimulates tumor angiogenesis, thus promoting tumor growth, invasion, and metastasis.255,256 Moreover, sphingosine kinase SK23–25 is overexpressed in tumor cells, while acid sphingomyelinase is downregulated, causing the disordered sphingolipid metabolism to affect lysosomal function and membrane structure and increasing lysosomal biogenesis.256–260