Rare EGFR Research Articles

Almonertinib and alflutinib show novel inhibition on rare EGFR S768I mutant cells.

EGFR classical mutations respond well to EGFR tyrosine kinase inhibitors. However, it is uncertain whether currently available EGFR-TKIs are effective against rare EGFR mutations and compound mutations. Herein, the effectiveness of almonertinib and alflutinib, the third-generation tyrosine kinase inhibitors developed in China, on rare EGFR S768I mutations and compound mutations is identified. In this study, using CRISPR method, four EGFR S768I mutation cell lines were constructed, and the sensitivity of EGFR to almonertinib and alflutinib was tested, with positive controls being the 1st (gefitinib), 2nd (afatinib), and 3rd (osimertinib) generation drugs. The present results indicate that almonertinib and alflutinib can effectively inhibit cell viability and proliferation in rare EGFR S768I mutations through the ERK or AKT pathways in a time-dependent manner, by blocking the cell cycle and inhibiting apoptosis. These findings suggest that almonertinib and alflutinib may be potential therapeutic options for non-small cell lung cancer patients with the EGFR S768I mutation.

First-line Osimertinib for Lung Cancer With Uncommon EGFR Exon 19 Mutations and EGFR Compound Mutations

IntroductionUp to 20% of EGFR-mutated NSCLC cases harbor uncommon EGFR mutations, including atypical exon 19 and compound mutations. Relatively little is known about the efficacy of osimertinib in these cases. MethodsPatients treated with first-line osimertinib for NSCLC with rare EGFR exon 19 (non E746_A750del) or compound mutations were included. Response assessment and time to progression were determined using Response Evaluation Criteria in Solid Tumors version 1.1 criteria. Kaplan-Meier analyses were used to estimate progression-free survival (PFS), time to treatment discontinuation (TTD), and overall survival (OS). ResultsThirty-seven patients with NSCLC harboring an atypical EGFR exon 19 mutation or compound mutation were treated with first-line osimertinib at Johns Hopkins from 2016 to 2021. Overall response rate (ORR) was 76% and median PFS, TTD, and OS were 13 months (95% confidence interval [CI]: 10–15), 22 months (95% CI: 17–32) and 36 months (95% CI, 29–48), respectively. Among atypical exon 19 mutations (n = 25), ORR was 80%, median PFS was 12 months (95% CI: 10–15), median TTD was 19 months (95% CI: 17–38), and median OS was 48 months (95% CI: 25–not reached). Compound mutations (n = 12) had an ORR of 67%, median PFS of 14 months (95% CI: 5–22), median TTD of 26 months (95% CI: 5–36), and median OS of 36 months (95% CI: 20–46). Twelve patients (32%) continued first-line osimertinib after local therapy for oligoprogression. ConclusionsOsimertinib exhibited favorable outcomes for rare EGFR exon 19 and compound mutations. The heterogeneity in outcomes among these groups of tumors with similar mutations underscores the need for continued reporting and further study of outcomes among rare variants to optimize management for each patient.

Prognostic and predictive biomarkers with therapeutic targets in nonsmall-cell lung cancer: A 2023 update on current development, evidence, and recommendation.

Since the publication of the original work in 2014, significant progress has been made in the characterization of genomic alterations that drive oncogenic addiction of nonsmall cell lung cancer (NSCLC) and how the immune system can leverage non-oncogenic pathways to modulate therapeutic outcomes. This update evaluates and validates the recent and emerging data for prognostic and predictive biomarkers with therapeutic targets in NSCLC. We performed a literature search from January 2015 to October 2023 using the keywords non-small cell lung cancer, clinical practice guidelines, gene mutations, genomic assay, immune cancer therapy, circulating tumor DNA, predictive and prognostic biomarkers, and targeted therapies. We identified, reviewed, and evaluated relevant clinical trials, meta-analyses, seminal articles, and published clinical practice guidelines in the English language. Regulatory-approved targeted therapies include those somatic gene alterations of EGFR ("classic" mutations, exon 20 insertion, and rare EGFR mutations), ALK, ROS1, BRAF V600, RET, MET, NTRK, HER2, and KRAS G12C. Data for immunotherapy and circulating tumor DNA in next-generation sequencing are considered emerging, whereas the predictive role for PIK3CA gene mutation is insufficient. Advances in sequencing and other genomic technologies have led to identifying novel oncogenic drivers, novel resistance mechanisms, and co-occurring mutations that characterize NSCLC, creating further therapeutic opportunities. The benefits associated with immunotherapy in the perioperative setting hold initial promise, with their long-term results awaiting.

215 Metastatic NSCLC adenocarcinoma with extremely rare EGFR exon 21 p. (Leu833_His835delinsValValLeu) mutation is clinically sensitive to Osimertinib

215 Metastatic NSCLC adenocarcinoma with extremely rare EGFR exon 21 p. (Leu833_His835delinsValValLeu) mutation is clinically sensitive to Osimertinib

Survival analysis of patients with advanced non-small cell lung cancer receiving EGFR-TKI treatment of Yunnan in southwestern China: a real-world study.

Patients with EGFR mutations who have advanced-stage non-small cell lung cancer (NSCLC) already receive tyrosine kinase inhibitors (TKIs) as the standard first-line therapy. Notably, Yunnan is a regional high incidence area of lung cancer in the highlands with a high rate of rare EGFR mutations. Overall, lung cancer patients in Xuanwei may present a distinct subgroup globally. Recent studies suggested that the NSCLC cohort in Xuanwei harbored a significantly higher uncommon mutation rate. However, little was known about the clinicopathological features and treatment efficacy of EGFR-TKI in Yunnan NSCLC patients. This study aimed to investigate the clinical impact of histologic type on the survival outcomes of patients with stage IIIB and IV NSCLC receiving EGFR-TKI treatment of Yunnan in southwestern China. In this retrospective study, we enrolled advanced NSCLC patients (IIIB-IV) with EGFR mutations who were first diagnosed and treated at Yunnan Cancer hospital from January 2016 to December 2019. Sociodemographics, lifestyle, survival, and clinicopathological characteristics of the patients were collected. The Kaplan-Meier method was used to assess the OS and PFS of patients. An analysis of prognostic factors was conducted using Cox regression. A total of 468 eligible patients were included. The median progression-free survival (PFS) and overall survival(OS) were 11.30(95% CI, 10.12-12.48) months and 30.30(95% CI, 26.24-34.36) months. Based on survival analysis among all the patients,females(HR=0.815;95% CI:0.671-0.989; P=0.017), Xuanwei origin (HR=0.776; 95% CI: 0.609-0.989; P=0.040), sample types(HR=0.780; 95% CI: 0.642-0.947; P=0.012) had a longer PFS. Multivariable analysis showed that only the sample type was an independent factor on median PFS with EGFR-TKI therapy. Patients less than 60 years old (HR=1.433; 95% CI:1.134-1.812, P=0.003)had better OS, but objectives with BMI≥24kg/m2(HR=0.653; 95% CI: 0.500-0.864; P=0.002), females(HR=0.776; 95% CI:0.613-0.982; P=0.035)and patients with tissue sample type (HR=0.760; 95% CI:0.600-.0961; P=0.022) had better OS. Notably, subgroup analysis of our study also found that PFS was significantly better in patients with G719X, L861Q, S768I, G719X+L861Q, and G719X+S768I in Xuanwei than classical mutation ones, including 19-Del and L858R (median 22.7 vs. 12.0 months, HR=0.523, P=0.010), while PFS was inferior in patients with rare mutations of EGFR in non-Xuanwei than the classical mutation ones (median 5.10 vs. 11.10 months, HR=1.760, P=0.015). NSCLC patients in Yunnan displayed a unique EGFR mutation profile, especially a higher prevalence of EGFR uncommon and compound mutations subtype. This study indicates prognostic factors of NSCLC treated with EGFR-TKI in Yunan and Xuanwei. This study will provide new clinical evidence for EGFR-TKI-targeted therapy in patients with rare EGFR mutations in China and worldwide. More researchs were needed for NSCLC EGFR-TKI therapy and medical insurance policy-making in Yunnan, Xuanwei area and uncommon especially.

EGFR assessment using next generation sequencing as a reflex testing on surgically resected non-squamous non-small cell lung carcinoma.

8539 Background: EGFR status assessment is mandatory in early stage (IB-IIIA) non-squamous non-small cell lung carcinoma (NS-NSCLC), but whether NGS methods should be used as reflex testing for this evaluation in daily practice is controversial. However, co-occuring mutations, notably TP53 mutations, may have an impact on tumor behavior and prognosis, and so, on future adjuvant therapeutic strategies. Methods: EGFR mutations were assessed prospectively using NGS (Oncomine Precision Assay genes panel) in 720 NS-NSCLC surgically resected between January 2021 and September 2022 in a single institution (LPCE, Nice, France). PD-L1 expression was evaluated in all tumors. Disease free survival (DFS) analysis was available in 675/720 (94%) patients. Results: EGFR mutations were detected in 83/720 (11.5%) cases. A common non-compound EGFR mutation (L858R or del19) was observed in 62/83 (75%) cases. 12/83 (14%) and 9/83 (11%) tumors had a rare non-compound and compound EGFR mutations, respectively. 40/83 (48%) has a co-occuring mutation, including a TP53 (30/40; 75%) mutation, mainly in exon 5, 7 or 8. EGFR/TP53 mutated tumors were significantly associated with higher PD-L1 expression compared to EGFR mutated tumors. A significant correlation was noted between worse DFS and the detection of a mutation in EGFR exon 18 mutation, as well as the detection of a co-mutation in TP53 exon 7 and in MET exon 14. Conclusions: Genomic alteration should be systematically evaluated using an NGS reflex testing in surgically resected NS-NSCLC, since future adjuvant therapeutic decision making may consider the presence of compound EGFR mutations as well as co-occuring mutations in other genes, especially in TP53.

Afatinib for the Treatment of NSCLC with Uncommon EGFR Mutations: A Narrative Review.

Afatinib, the world's first irreversible ErbB family (containing four different cancer cell epidermal growth factor receptors, including EGFR, HER2, ErbB3, and ErbB4) inhibitor, is a second-generation oral epidermal growth factor receptor tyrosine kinase inhibitor (EGFR-TKI). It can be used as a first-line treatment for locally advanced or metastatic non-small-cell lung cancer (NSCLC) with an EGFR-sensitive mutation or for patients with locally advanced or metastatic squamous lung cancer whose disease progresses during or after platinum-containing chemotherapy. Currently, with the use of third-generation EGFR-TKIs, afatinib is no longer clinically indicated as the first choice for patients with NSCLC who have EGFR-sensitive mutations. However, afatinib showed a considerable inhibitory effect in NSCLC patients with uncommon EGFR mutations (G719X, S768I, and L861Q) according to a combined post hoc analysis of the LUX-Lung2/3/6 trials. With the development of genetic testing technology, the detection rate of uncommon EGFR mutations is increasing. The aim of this paper is to describe in detail the sensitivity of rare EGFR mutations to afatinib and to provide information and a reference for those suffering from advanced NSCLC who have uncommon EGFR mutations.

Identification of a rare EGFR exon 18 mutation in lung adenocarcinoma using targeted next-generation sequencing as a tool for precision medicine

Identification of a rare EGFR exon 18 mutation in lung adenocarcinoma using targeted next-generation sequencing as a tool for precision medicine

Efficacy of EGFR-Tyrosine Kinase Inhibitors for advanced non-small cell lung cancer patients harboring rare EGFR mutations of exon 18 E709X.

EGFR-tyrosine kinase inhibitors (TKIs) show efficacy against lung cancer, and afatinib has been used as a standard therapy for patients with non-small cell lung cancer (NSCLC) with EGFR rare mutations such as S768I, G719X, and L861Q. However, the efficacy of EGFR-TKIs against NSCLC with EGFR rare mutations of exon 18 E709X has been less studied. The present study aimed to analyze the efficacy and safety of EGFR-TKIs in NSCLC patients with rare mutations. Our study enrolled 15 NSCLC patients with exon 18 E709X mutation who were admitted to Zhejiang Cancer Hospital. The objective response rate (ORR), progression-free survival (PFS), overall survival (OS), and treatment-related adverse events (TRAEs) were analyzed. The ORR of the entire cohort of patients was 33.3%. The PFS of all patients with exon 18 E709X mutations was 10.9months. The OS was not reached. The PFS of patients with exon 18 E709-T710delinsD and E709A/G/K mutations showed no significant difference (5.3 vs. 13.5months, P = 0.238). A significant difference in OS was observed between patients with exon 18 E709-T710delinsD mutation and those with E709A/G/K mutation (12.2months vs. not reached, P = 0.029). No significant difference in efficacy was observed between second- and third-generation TKIs for NSCLC patients with exon 18 E709X mutations (PFS: 13.5 vs. 10.9months, P = 0.774; OS: 17.1months vs. not reached, P = 0.072). New treatment-related adverse events were not observed. NSCLC patients with exon 18 E709X mutations may benefit from treatment with second- or third-generation EGFR-TKIs.

Validation of a highly sensitive Sanger sequencing in detecting EGFR mutations from circulating tumor DNA in patients with lung cancers

BackgroundThe novel method, named blocker displacement amplification (BDA) Sanger, was applied to detect low variant allele frequency mutations in the circulating tumor DNA (ctDNA). This study aimed to evaluate the performance of the BDA Sanger method for the EGFR mutation detection in the ctDNA from lung cancer patients. MethodsA total of 195 plasma samples of lung cancer patients were included. The EGFR mutation status in the ctDNA was detected by the BDA Sanger and Super-ARMS assays. Next-generation sequencing (NGS) was further used to verify the mutant of EGFR with inconsistencies. ResultsBDA Sanger assay was capable of detecting EGFR mutations with a 0.20% VAF from plasma samples. Among treatment-naive patients with paired tissue and plasma samples, the EGFR positive percent agreement (PPA) was 79% by BDA sanger. EGFR mutation was detected in 34.4% (67/195) ctDNA samples by the Super-ARMS and in 41.0% (80/195) ctDNA samples by the BDA Sanger assay. The overall concordance rate between the BDA Sanger and Super-ARMS assays was 82% (160/195). The BDA Sanger also enabled the detection of rare EGFR mutations, which were not discovered by the Super-ARMS. ConclusionThe results supported the validity and efficiency of the BDA Sanger method for EGFR detection in patients with lung cancer, indicating that BDA Sanger has a great potential for application in detecting mutations in the ctDNA.

EP08.02-065 Response to Systemic Anti-Cancer Therapy in Uncommon EGFR Mutations

Exon 19 deletions, exon 21 L858R and exon 20 insertions represent the most frequent alterations in EGFR mutated non-small cell lung cancer (NSCLC). These alterations now all have approved targeted therapies. In contrast, there is limited data assessing activity of EGFR-directed therapy for uncommon EGFR alterations. We sought to describe clinical outcomes of patients with rare EGFR mutations that received systemic anticancer therapy (SACT) at our institution.

EP11.01-003 Advanced Non Small Cell Lung Cancer With EGFR Exon 20 Insertion Gene Mutation

The EGFR Exon 20 Inserton mutation is belongs to the group of rare EGFR mutations and that is resistant to TKIs generation I-II-III. We conduct research with the following objectives: a. Survey on the rate of EGFR Exon 20 Insertion mutations in patients with advanced NSCLC. b. Survey of subtypes of EGFR mutations Exon 20 Insertion offers applications in clinical practice.

Evaluation of Treatment Efficacy of Tyrosine Kinase Inhibitors in Rare Single EGFR Exon 21 L861Q Mutation: Single Center Experience.

OBJECTIVE:Epidermal growth factor receptor mutations are the second most common oncogenic driver event in non-small cell lung cancer. We aimed to compare the first generation erlotinib treatment with the second generation afatinib treatment in patients with non-small cell lung cancer with epidermal growth factor receptor exon 21 L861Q mutation.MATERIAL AND Methods:Progression-free survival and overall survival of 30 non-small cell lung cancer patients treated with erlotinib or afatinib due to single epidermal growth factor receptor L861Q positivity were compared retrospectively. The number of patients included in the first, second, and third treatment line was 15 (50.0%), 11 (36.7%), and 4 (13.3%), respectively.Results:There were 23 patients in the erlotinib arm and 7 patients in the afatinib arm. Median progression-free survival was 12.8 months in the erlotinib group and 9.3 months in the afatinib group. Median overall survival in erlotinib and afatinib groups was 77.9 months and 30.3 months, respectively. No statistically significant difference was found in the comparison of these survival times. Conclusion:Survival times of erlotinib and afatinib treatment are similar in patients with a single epidermal growth factor receptor L861Q mutation. In patients receiving tyrosine kinase inhibitors treatment, the female gender has a positive effect on progression-free survival, and being a non-smoker has a positive effect on overall survival. In patients with rare mutation exon 21 L861Q positivity, both first-generation and second-generation tyrosine kinase inhibitors should be considered.

Abstract 527: A streamlined workflow for liquid biopsy extraction and highplex digital PCR analysis using the Maxwell® RSC system and 6-color Crystal Digital PCR™

Abstract Circulating cell free DNA (cfDNA) extracted from liquid biopsy samples have become established sample types for characterizing oncology targets. Currently, there are several extraction protocols and genomic platforms for researchers to select when interrogating genetic information. The focus of this work was to identify a flexible method for sample extraction that seamlessly integrates into a straightforward and sensitive genetic analysis workflow from plasma samples. Here, we present a workflow combining the Maxwell RSC system for automated cfDNA extraction and Crystal Digital PCR on the naica system for ultrasensitive high-plex detection from liquid biopsy samples of EGFR mutations in non-small cell lung cancer (NSCLC) and PIK3CA mutations and HER2 amplification in breast cancer. By bridging sample extraction with the Maxwell RSC system and high-plex digital PCR with the 6-color naica® system, we detected with high sensitivity and precision 32 common and rare somatic EGFR mutations in exons 18, 19, 20, and 21, representing more than 90% of EGFR mutations described in NSCLC. Furthermore, following the same extraction and sample testing workflow, we simultaneously detected a set of PIK3CA mutations and HER2 amplification from cfDNA samples. This proof-of-concept workflow creates the foundation for further development of streamlined sample-to-answer protocols that will better assist cancer researchers across the biomarker testing landscape. Citation Format: Cécile Jovelet, Myrtille Remy, Mylene Menanteau, Doug White, Douglas Horejsh, Allison Mallory. A streamlined workflow for liquid biopsy extraction and highplex digital PCR analysis using the Maxwell® RSC system and 6-color Crystal Digital PCR™ [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 527.

Abstract 4113: Response to amivantamab, a bispecific EGF and MET receptor directed antibody, in a patient with an atypical EGFR mutated (G719X) non-small cell lung cancer (NSCLC) with leptomeningeal disease who progressed on osimertinib

Abstract Amivantamab is a bispecific antibody against EGF and MET receptors, approved for patients with locally advanced or metastatic NSCLC harboring EGFR exon 20 insertion after disease has progressed on or after platinum-based chemotherapy. Existing data is insufficient in establishing its efficacy on other rare EGFR mutated subtypes, central nervous system (CNS), or its resistance to 3rd generation tyrosine kinase inhibitor (TKI), osimertinib. Here, we report a case showing a good response on single agent amivantamab in an atypical EGFR mutation (G719A, exon18 substitution) NSCLC that progressed to CNS involvement on osimertinib. A 67-year-old male presented with stage IVB squamous cell carcinoma of lung with osseous metastases. CT chest, abdomen, and pelvis revealed a speculated 7.7 cm right upper lung lesion with hilar and subcarinal lymphadenopathies. MRI brain and spine showed multiple bone metastases without CNS involvement. Tissue biopsy confirmed poorly differentiated squamous cell carcinoma with PD-L1 IHC 75%. Tissue next generation sequencing (NGS) showed EGFR G719A. He was started on osimertinib. Two months later, he was hospitalized for drug-induced pneumonitis which prompted off osimertnib. CT angiogram chest showed new diffuse pericardial thickening and nodularity, suggestive of progressive disease. Two cycles of chemotherapy were delivered followed by immunotherapy with ipilimumab and nivolumab. In 10 weeks, progression of disease was revealed in MRI brain demonstrating new parenchymal and leptomeningeal metastases. Amivantamab monotherapy was initiated with discontinuation of immunotherapy. The patient tolerated amivantamab without major complications. His performance status remained the same before and after amivantamab. He denied fatigue, anorexia, nausea or vomiting, however, endorsed rash, which was managed with hydrocortisone cream. Repeat scans in 6 weeks showed decreased leptomeningeal enhancement, and reduction in the size of parenchymal lesions, lung mass, and lymphadenopathies. The highest variant allele fraction from circulating tumor DNA NGS assay from Guardant360 was significantly improved on amivantamab from 25.6% (EGFR G719A), at time of diagnosis, to non-detectable. Amivantamab monotherapy has shown an encouraging outcome in a patient with an atypical EGFR mutated (G719X) NSCLC with leptomeningeal disease who progressed on osimertinib. Our case has shown significant response on CNS involvements, which is contrary to known poor blood-brain barrier penetration of amivantamab. This supports current trial evaluating the efficacy of amivantamab for NSCLC with rare EGFR mutations such as G719X, and ones progressed on 3rd Gen TKI treatment. Additional studies evaluating the efficacy of amivantamab on CNS metastasis are warranted. Citation Format: Jinah Kim, Horyun Choi, Yeun Ho Lee, Leeseul Kim, Young Kwang Chae. Response to amivantamab, a bispecific EGF and MET receptor directed antibody, in a patient with an atypical EGFR mutated (G719X) non-small cell lung cancer (NSCLC) with leptomeningeal disease who progressed on osimertinib [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 4113.

Real-life comparison of afatinib and erlotinib in non-small cell lung cancer with rare EGFR exon 18 and exon 20 mutations: a Turkish Oncology Group (TOG) study.

To compare the survival of first- and second-generation tyrosine kinase inhibitors (TKIs) in patients with rare EGFR exon 18 and exon 20 mutation-positive non-small cell lung cancer (NSCLC). We retrospectively evaluated survival characteristics of 125 patients with EGFR exon 18 and exon 20 mutated NSCLC who received erlotinib or afatinib as first line treatment between 2012 and 2021 from 34 oncology centres. Since exon 20 insertion is associated with TKI resistance, these 18 patients were excluded from the study. EGFR exon 18 mutations were seen in 60%, exon 20 mutations in 16%, and complex mutations in 24% of the patients with NSCLC who were evaluated for the study. There were 75 patients in erlotinib treated arm and 50 patients in afatinib arm. Patients treated with erlotinib had progression-free survival time (PFS) of 8.0months and PFS was 7.0months in the afatinib arm (p = 0.869), while overall survival time (OS) was 20.0 vs 24.8months, respectively (p = 0.190). PFS of exon 18 mutated arm was 7.0months, exon 20 mutated arm was 4.3months, and complex mutation positive group was 17.3months, and this was statistically significant (p = 0.036). The longest OS was 32.5months, seen in the complex mutations group, which was not statistically different than exon 18 and in exon 20 mutated groups (21.0 and 21.2months, respectively) (p = 0.323). In this patient group, especially patients with complex mutations are as sensitive to EGFR TKI treatment similar to classical mutations, and in patients with rare exon 18 and exon 20 EGFR mutation both first- and second-generation EGFR-TKIs should be considered, especially as first- and second-line options.

P8‐120: Therapeutic efficacy of osimertinib following afatinib for the rare EGFR mutation exon19 delL747_P753insS: A case report

P8‐120: Therapeutic efficacy of osimertinib following afatinib for the rare EGFR mutation exon19 delL747_P753insS: A case report

High Tumor Mutational Burden in Rare and Complex EGFR Mutant Non-Small Cell Lung Cancer

<h3>Purpose/Objective(s)</h3> Classical EGFR mutant lung cancer with exon 19 deletions, exon 21 L858R and de novo exon 20 T790M mutations are associated with good response to tyrosine kinase inhibitors. In contrast, rare and complex mutations have uncertain or poor response to targeted therapy. Recent retrospective analyses have observed a potential benefit of rare and complex EGFR mutations from immunotherapy, in contrast to cancers harboring classical EGFR mutations. We hypothesized that a larger proportion of rare and complex EGFR mutant lung cancers may have molecular differences that would promote immune checkpoint blockade as a putative combination or alternative treatment. <h3>Materials/Methods</h3> Patients (pts) with nonsynonymous EGFR mutant lung cancers from two datasets (The Cancer Genome Atlas, Clinical Proteomic Tumor Analysis Consortium) were identified. Rare EGFR mutations were defined as non-sensitizing somatic mutations occurring within the tyrosine kinase (TK) domain of exons 18 through 21. Complex EGFR mutant cases (i.e., G719X + S768I) were tumors with two mutations within the TK region where at least one mutation was non-sensitizing. Tumor mutational burden (TMB) was calculated as the number of somatic mutations per million bases (human exome was estimated to be 38 Mb). High-TMB was denoted as a TMB over 10. Gene expression of PD-L1 was evaluated by RNA-sequencing as well as bioinformatic assessment of tumor purity, immune infiltration and stroma contribution within the tumor microenvironment using the ESTIMATE (Estimation of STromal and Immune cells in MAlignant Tumours using Expression data) algorithm. <h3>Results</h3> Of the 675 pts evaluated, 97 (14.3%) had tumors which harbored EGFR mutations. Patients with EGFR mutant tumors were more likely to be female (64 vs 48%, <i>P</i> = 0.006) and non-smokers (49 vs 12%, <i>P</i> < 0.001). Tumors from non-smokers were less likely to have high-TMB (<i>P</i> < 0.001). Twenty four of 97 (25%) EGFR mutant cancers had either rare (n = 12) or complex mutations (n = 12). Tumors with rare/complex EGFR mutations had a higher average TMB (5.4 compared to 2.3) and were significantly more likely to have a TMB over 10 (17% vs 1.4%, <i>P</i> = 0.003). 25% of rare EGFR mutant tumors (L861Q, E866K, K754I) had a TMB > 10 (<i>P</i> = 0.0003). There were no significant differences in PD-L1 expression (<i>P</i> = 0.46) or smoking history (<i>P</i> = 0.71) between classical and rare/complex EGFR mutant cancers. Tumors with rare EGFR mutations had significantly higher tumor purity (0.759 versus 0.459, <i>P</i> = 0.0038), and corresponding lower proportion of immune (<i>P</i> = 0.0045) and stromal cells (<i>P</i> = 0.0077). <h3>Conclusion</h3> Our data suggests that lung cancers harboring rare EGFR mutations may have mutation-specific dependencies that would make a non-significant proportion amenable to immunotherapy. While PD-L1 appears to be a poor biomarker, we observed an increase in high-TMB and distinct changes in the tumor microenvironment in rare EGFR mutant lung cancer.

Resistance mechanisms to osimertinib and emerging therapeutic strategies in nonsmall cell lung cancer.

This review aims to introduce the resistance mechanisms to osimertinib, discuss the therapeutic strategies, and make clinical updates in overcoming resistance to osimertinib. Osimertinib has shown favorable efficacy on second-line and first-line treatments in EGFR-mutant advanced nonsmall cell lung cancer (NSCLC). However, the presence of primary and acquired resistance to osimertinib restricts its clinical benefits. The primary resistance mainly consists of BIM deletion polymorphism and EGFR exon 20 insertions. Meanwhile, the heterogeneous mechanisms of acquired resistance include EGFR-dependent (on-target) and EGFR-independent (off-target) mechanisms. EGFR C797S mutation, MET amplification, HER2 amplification, and small cell lung cancer transformation were identified as frequent resistance mechanisms. Recently, more novel mechanisms, including rare EGFR point mutations and oncogenic fusions, were reported. With the results of completed and on-going clinical trials, the emerging therapeutic strategies of postosimertinib progression are summarized. The resistance mechanisms to osimertinib are heterogeneous and gradually perfected. The combination of osimertinib with bypass targeted therapy and other therapeutic approaches emerge as promising strategies.

Targeted therapy of non-small cell lung cancer with rare EGFR gene mutations

Targeted therapy of non-small cell lung cancer with rare EGFR gene mutations