Background: TMB, a measurement of the number of mutations carried by tumor cells, is emerging as a biomarker for the identification of patients who may benefit from certain I-O-based therapies. TMB-high (TMB-H) tumors, defined by the detection of ≥10 mutations/megabase (mut/Mb) in tumor cells using a tissue-based assay such as the FoundationOneCDx (F1CDx) assay (Foundation Medicine, Inc.), may be more likely to respond to some I-O therapies. Higher neoantigen loads of TMB-H tumors have been proposed to contribute to increased responsiveness of TMB-H tumors to certain I-O therapeutics. Pembrolizumab was approved by the FDA on June 16, 2020 for the treatment of adult and pediatric patients with unresectable or metastatic TMB-H tumors, as determined by F1CDx, based on results from the KEYNOTE-158 trial (NCT02628067), which demonstrated that 50% of patients with TMB-H tumors had response durations of ≥24 months, with objective response rates in TMB-H vs. non-TMB-H patients of 29% and 6%, respectively (Marabelle et al, The Lancet Oncology, 2020). This survey-based study aimed to evaluate awareness and utilization of TMB as a biomarker for I-O therapeutics among practicing community oncologists in the U.S. Methods: Questions related to awareness and utilization of TMB as a biomarker for I-O therapeutics were developed by two medical oncologists (AG and BF) and presented to community oncologists in a web-based survey prior to virtual meetings held between October and November 2020. Descriptive statistics were used to analyze the results. Results: Of the 193 participating providers geographically distributed across the U.S., 15% reported being unaware of either the concept of TMB in I-O therapy or how to use the information clinically. 39% of these providers reported testing ≤25% of patients with advanced cancer for TMB, including 8% who do not test for TMB at all. Misconceptions regarding TMB identified among participating providers included the belief that high TMB is considered to be > 5 mut/Mb among 20% of providers, that TMB is essentially the same as MSI-high among 8% of providers, and that there are no therapies with FDA approval based on TMB among 15% of providers. Further, 37% of the participants did not identify pembrolizumab as an agent approved for the treatment of solid tumors based on TMB-H status. Conclusions: These findings demonstrate that there is a knowledge gap regarding the definition of TMB, testing for TMB, as well as implementation of TMB status in clinical decision making. Education directed towards community oncology providers regarding TMB and its use as a predictive biomarker for I-O therapy may improve its utilization and adoption in solid tumors to improve patient outcomes.