Highs, lows of tumor mutation burden testing
September 2022—It may not be the oldest story in the world, but in clinical laboratories it’s an oft-told tale: Tumor meets biomarker; drug meets companion diagnostic; both meet FDA approval; clinicians meet with patients offering new hope—and those in the lab are left trying to figure out how to make it all work. That story is playing out again in the realm of measuring tumor mutational burden. In mid-2020 the FDA approved pembrolizumab as a new treatment option in adult and pediatric patients with TMB-high (≥10 mutations/megabase) solid tumors, as determined by the FDA-approved FoundationOne CDx assay. “That doesn’t sound too controversial, right?” says Alain Borczuk, MD, vice chair of anatomic pathology and director of oncologic pathology, Northwell Health Cancer Institute. “It’s not the only way in, but it’s one of the ways in. If you’re arguing for your patient that this is the biomarker that makes them eligible for the drug, then the next questions will be, What was the number? And what was the test?” And it’s off to the races.