Molecular pathology selected abstracts
March 2021—High tumor mutational burden in certain cancers has become an established biomarker for predicting a response to immune checkpoint inhibitor therapy and longer overall survival after such treatment. The immune checkpoint inhibitor (ICI) pembrolizumab, for example, has recently been approved by the FDA for patients whose solid tumors, regardless of histology, have a high tumor mutational burden (TMB), defined as 10 or more mutations per megabase. TMB, assessed by next-generation sequencing, varies considerably among cancers and can range from 0.01 to more than 1,000 somatic mutations per megabase of sequenced genome. The presumed mechanism for the enhanced responsiveness to immunotherapy associated with high TMB is the creation, by somatic mutation, of potentially immunogenic neoantigens that facilitate an enhanced antitumor immune response. Given this presumed mechanism, the authors addressed whether high TMB levels, which are associated with better cancer outcomes in patients treated with immune checkpoint inhibitors, might also lead to better outcomes for patients treated with other anti-cancer therapies.