Downregulation of ASS1 caused by promoter methylation increases the susceptibility of tumor cells to PEGylated arginine deiminase (ADI-PEG20) (Table 1), a drug for arginine-deprivation treatment that has been used in clinical trials for a variety of tumors (Delage et al., 2012; Syed et al., 2013; Mcalpine et al., 2014). This evidence concerns the gene ASS1 and neoplasm.