Analytical Validation of Blood-Derived Tumor Mutation Burden (bTMB) Assays: A Joint Consensus Recommendation of the BLOODPAC bTMB Analytical Validation Working Group.

Immunotherapies have changed the treatment paradigm for patients with advanced and metastatic solid tumors, with tumor mutation burden representing one approach to identify patients who may experience clinical benefit. Circulating tumor DNA-based approaches have been developed for comprehensive analyses of clinically actionable biomarkers; however, blood tumor mutation burden (bTMB) represents a novel, complex biomarker. Although the clinical utility of bTMB is an evolving area of active development and has not led to consistent conclusions across studies, robust analytical validation of the underlying test is important to ensure that technical and biological limitations do not confound clinical interpretation of these results. To this end, the BLOODPAC bTMB Analytical Validation Working Group sought to identify key technical and biological issues associated with analytical validation of bTMB tests, along with a conceptual framework to address these challenges. This publication provides guidance for device manufacturers to demonstrate analytical performance of their test with the understanding that these data would be accompanied by an appropriately designed clinical validation study to demonstrate performance within the intended use population. Therefore, the specific algorithm to determine the bTMB result, along with the associated cutoff, is out of scope of this Perspective. Device manufacturers should also ensure that appropriate pre-analytical variables are accounted for and methods are incorporated to differentiate tumor-specific alterations from those associated with germline polymorphisms or clonal hematopoiesis.