MMR mutations occurring after TMZ administration may occur either through the selection of MMR-deficient subclones already present in the heterogeneous tumor cell population or by TMZ directly inducing mutation in an MMR gene, particularly in tumor cells with methylated MGMT [17, 31, 45, 53, 94, 102, 107, 179, 209, 213, 217, 233]. The gene discussed is MRC1; the disease is neoplasm.