ASS1 and cancer: ASS1 expression has been reported to be decreased or even abolished in many cancers (Dillon et al., 2004), especially in malignant melanoma (Feun et al., 2012), HCC (Delage et al., 2010), and prostate cancer (Kim et al., 2009), which are thought of as arginine-auxotrophic cancers because of the inability to synthesize arginine and resulting susceptibility to arginine-deprivation therapy.