Previous studies have found 42 tumors harboring IDH1 mutations by screening 15,531 prostate cancers (0.3%) or 43 tumors exhibiting CD117 overexpression in a cohort of 1654 breast carcinomas (2.6%).33,34 It is of note that only four of six cancers that were initially suspected to have MSI were confirmed in a subsequent large section validation. The gene discussed is IDH1; the disease is cancer.