Pegylated ADI, namely ADI-PEG20, not only acts effectively against a variety of cancer cell lines deficient in argininosuccinate synthetase (ASS) [2,5,6,7], but also yields promising results in phase II/III studies in patients with hepatocellular carcinoma (HCC) [8,9] and melanoma [10,11]. This evidence concerns the gene ASS1 and hepatocellular carcinoma.