Tumor mutational burden (TMB) is a [[genomic]] [[biomarker]] with the potential to make a significant impact on the landscape of cancer immunotherapy. This emerging marker measures the number of mutations within a tumor genome and has already been shown to be associated with improved responses to [[checkpoint inhibitor]]s.

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It is defined as the number of non-inherited mutations per million bases of investigated genomic sequence, and its measurement has been enabled by next generation sequencing.