In addition to its role as a predictive biomarker for arginine deprivation therapy, ASS1 deficiency is increasingly recognized as a prognostic biomarker for poor survival outcomes in several cancer types, including mesothelioma, sarcomas, bladder, ovarian, and breast cancer by driving increased tumor cell proliferation, invasiveness, and metastasis.8, 9, 10, 11, 12, 13, 14. The gene discussed is ASS1; the disease is mesothelioma.