GLUL and plasma cell myeloma: More recently, other examples have been described in human cancers, such as the loss of argininosuccinate synthetase in hepatocellular carcinomas, metastatic melanomas, and other cancers, leading to auxotrophy for arginine (19), and the absence of glutamine synthetase expression in multiple myeloma (20) and oligodendroglioma (21), leading to Gln auxotrophy.