Real-world genetic testing outcomes of pan-cancer testing for mismatch repair deficiency.

Pan-cancer MMR testing for pembrolizumab consideration can identify LS cases at a rate similar to universal CRC and EC screening programs. A persistent challenge is subsequent uptake of genetic testing. MMR testing should be prioritized in brain and small intestinal tumors, and multigene panel testing is recommended in patients with dMMR, as unexpected pathogenic variants in non-LS genes were found as frequently as LS gene variants.