In sporadic, nonhereditary CRC, MSI is frequently observed due to epigenetic silencing of MLH1 (Cunningham et al., 1998; Herman et al., 1998; Kane et al., 1997; Kuismanen et al., 2000). MSI-high (MSI-H) tumors display a hypermutator phenotype (Cancer Genome Atlas Network, 2012), which entails increased immunogenicity, amendable to therapy with immune checkpoint inhibitors (Le et al., 2015). The gene discussed is MLH1; the disease is colorectal carcinoma.