[Research Progress on Heterogeneity of Tumor Mutation Burden in Patients with 
Non-small Cell Lung Cancer]

Programmed death ligand 1 (PD-L1) is a well known biomarker for targeted immunotherapy. However, the relationship between the expression of PD-L1 and the immunotherapy efficacy is not always consistent in different cases. Some patients who are PD-L1 negative still can benefit from immunosuppressive therapy, while some non-small cell lung cancer (NSCLC) patients with PD-L1 positive, even strongly positive, can not. Therefore, PD-L1 is not a completely reliable immunotherapy biomarker. Tumor mutation burden (TMB) estimated by whole exome sequencing (WES) is a biomarker recently approved by Food and Drug Administration (FDA). In this paper, we briefly reviewed the factors that result in the variaty of TMB in order to improve the reliability of the TMB and help clinicians to select patients who can get benefit from immunotherapy more wisely.
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