A minimum of 93% of ovarian cancer TCGA cases and 66% of colorectal cancer TCGA cases had alterations (not considering predicted deleterious missense mutations) affecting one or more GIS gene homologues, with only 5 and 8% of the samples, respectively, having alterations in genes expected to cause a strong MMR defect (MSH2, MSH6, MLH1 and PMS2) and hence a mutator phenotype. The gene discussed is MSH2; the disease is colorectal cancer.