MGMT and cancer: MGMT activity was uniformly high in primary lymphocytes, with % reporter expression generally less than 0.1%, comparable to a previously reported positive control, TK6+MGMT.[44] By contrast, MGMT activity was highly variable in LCLs;[9] indeed, for some LCLs, MGMT activity was less than 5% of the level observed in a TK6+MGMT positive control.[44] MGMT silencing in cancer has long been known,[45] but these findings suggest it can occur in immortalized cells outside the context of carcinogenesis.