ASS1 and malignant pleural mesothelioma: Epigenetic silencing via methylation of the CpG islands within the ASS1 promoter accounts for loss of ASS1 expression in many solid tumors studied to date, including ovarian, malignant pleural mesothelioma, glioblastoma, myxofibrosarcoma and bladder, as well as in some lymphoid malignancies [4, 22–24, 26, 27].