ASS1 and breast carcinoma: Many human malignancies including malignant melanoma, hepatocellular carcinoma, prostate cancers, mesothelioma, small cell lung cancer, and breast cancers, do not produce sustainable amounts of arginine (Arg), because the rate-limiting enzyme for biosynthesis of Arg, argininosuccinate synthetase 1 (ASS1), is silenced [1].