 High tumor mutational burden, TMB, is an emerging biomarker of sensitivity to immune checkpoint inhibitors. The distribution of TMB and subset of patients with high TMB has not been well characterized in the majority of cancer types. TMB increases significantly with age, showing a 2.4 fold difference between age 10 and age 90 years. This article was authored by Zachary Archalmers, Caitlyn F Connolly, David Fabrizio, and others.