Tumor mutation burden (TMB) is an independent indicator used to select patients sensitive to immunotherapy. The present study aimed to investigate the clinicopathological and molecular characteristics of patients with hypermutant lung cancer to identify an economical, simple and complementary method for predicting TMB and immunotherapy responses. In total, 1,000 patients with lung cancer were randomly selected, and their samples were submitted to next-generation sequencing, with their TMB status reviewed. The threshold of hypermutation was set to 17.24 mutations (muts)/Mb. The proportion of smokers was higher in the hypermutant cohort (n=67) compared with in the non-hypermutant cohort (n=933; 85.1 vs. 46.6%; P<0.0001). Compared with in the non-hypermutant cohort, the proportion of squamous cell carcinoma cases and small cell lung cancer cases was higher in the hypermutant cohort (22.4 vs. 13.1% and 6.0 vs. 2.6%, respectively). In addition, compared with in the non-hypermutant cohort, mutations in the low-density lipoprotein receptor-related protein 1B were more frequently observed in the hypermutant cohort (67.2 vs. 14.3%; P<0.0001). A similar trend was obtained for all genes tested, except for the EGFR gene. Furthermore, in the hypermutant cohort, the prevalence of microsatellite instability was extremely high (9.0%). The mutation frequency in DNA damage response (DDR) genes was notably higher in the hypermutant cohort, where several DDR-associated genes were enriched, compared with in the non-hypermutant cohort. The enrichment analysis revealed a strong association between mutations in Notch signaling and high TMB. To the best of our knowledge, the present study is the first to comprehensively investigate the clinical and genetic characteristics of patients with hypermutant lung cancer in a Chinese population. The results of the current study suggested that hypermutant lung cancer exerted distinctive clinical and genetic features, which may be used as complementary indicators for screening patients sensitive to immunotherapy.

e21646 Background: Identifying targetable genetic variants may help maximize clinical benefit of non-small cell lung cancer (NSCLC). Here, we retrospectively analyzed the benefit of next-generation sequencing (NGS) for NSCLC in routine clinical practice. Methods: A total of 59 NSCLC patients were enrolled in the study from Jun. 2018 to Dec. 2019. Formalin-fixed paraffin-embedded tissues samples were collected and sequenced by NGS, which detects single-nucleotide variants, small insertions/deletions, rearrangements, and copy-number alterations of either 59 or 1021 tumor related genes. The tumor response was evaluated using RECIST v1.1. Results: The detection rate of targetable variants was 59.32% (35/59), including EGFR mutation 49.15% (29/59), ALK rearrangement 5.08% (3/59), ROS1 rearrangement 1.69% (1/59), BRAF V600E mutation 1.69% (1/59), and ERBB2 mutation 1.69% (1/59). Of 29 patients with EGFR mutations, 5 patients (17.24%) had multiple EGFR mutations, including 2 patients (6.89%) with uncommon mutations. 25patients (86.21%) harbored concurrent mutations that may limit the efficacy of EGFR-TKIs, including EGFR amplification, activation of bypass signaling pathways, TP53 exon8 mutation, BCL2L11 deletion polymorphism, and PI3K-AKT-mTOR and cell cycle gene alterations. Among 25 patients received EGFR-TKIs, TKI effectiveness was evaluated in 18 patients. The disease control rate was 100% and overall response rate was 27.78%. The proportion of patients with TMB-H and/or PD-L1≥1, and targetable variants negative was 33.89% (20/59). Only one patient of this group received immunotherapy with pembrolizumab and achieved SD at the 2nd month. The proportion of patients with targetable variants negative, TMB-L, and PD-L1 < 1 or unknow patients was 6.78% (4/59), two patients of them left hospital without additional treatment, two patients received chemotherapy and the KRAS mutation present in one of them suggested that he might be resistant to EGFR-TKIs. Conclusions: More than half of NSCLC patients have targetable genetic variants and more than 30% patients have a molecular signature that can be treated with immunotherapy. Compared with immunotherapy, targeted therapy has higher acceptability in real-world. NGS-based genetic testing may have clinical value to predict the effectiveness of targeted therapy and immunotherapy. It can be widely implemented and standardized into clinical use.

e15255 Background: Tumor mutation burden (TMB) has been confirmed to predict the sensitivity to immunotherapy across multiple tumor types. Multiple genetic factors have been confirmed to increase the level of TMB, such as mutations in DNA damage repair (DDR) genes, POLE/POLD1, and high microsatellite instability (MSI). However, the extent that these factors contribute to hypermutation in lung cancer has not been fully investigated. Methods: We retrospectively reviewed the genetic profiles of 1000 lung cancer patients (pts) who underwent 1021-panel matched tumor-normal next-generation sequencing using tumor tissue samples and peripheral blood. Their TMB status were analyzed to determine the threshold of hypermutation. The clinicopathological characteristics, genetic profiles and genetic factors related to hypermutation were investigated for the pts in hypermutant cohort. Results: The threshold of hypermutation was determined as 19 muts/MB (top 5% in 1000 pts). As a result, 53 pts were included in the hypermutant cohort. A total of 1725 nonsynonymous somatic variants in 506 genes were identified. The most frequently mutated genes included TP53 (88.7%), LRP1B (71.7%), MLL2 (35.8%), EPHA5 (34.0%), and FAT1 (34.0%). KRAS was mutated in 17% pts, whereas mutations in EGFR, BRAF, ERBB2, MET were identified less commonly. MSI-high was observed in 5 cases. A germline mutation in BRCA1 gene was identified in an adenocarcinoma patient. Compared to genetic profiles of non-small cell lung cancer from TCGA database, mutations in multiple DDR genes were enriched in the hypermutant cohort (Table). No known driver mutation in POLE/POLD1 was identified. Conclusions: MSI-high and mutations in DDR genes may be associated with high level of TMB, whereas POLE/POLD1 driver mutations may not be related to hypermutant lung cancer. Hypermutant lung cancer displays distinctive molecular features that may be used as complementary indicators to screening pts sensitive to immunotherapy. [Table: see text]