Constitutional mismatch repair deficiency (CMMRD) syndrome, a rare condition that greatly increases the risk of cancers among children, adolescents, and young adults [1], is caused by biallelic (homozygous or compound heterozygous) germline pathogenic variants in one of the mismatch repair (MMR) genes (MLH1, MSH2, MSH6, and PMS2). Here, PMS2 is linked to cancer.