Many tumors, including HCC, malignant melanoma, malignant pleural mesothelioma, and prostate and renal cancers, are arginine auxotrophic due to their variable loss of argininosuccinate synthase 1 (ASS1), which is severely reduced or absent in numerous types of aggressive and chemoresistant cancers. This evidence concerns the gene ASS1 and malignant pleural mesothelioma.