EGFR C797S Research Articles

Phase 1/2 study of BLU-451, a central nervous system (CNS) penetrant, small molecule inhibitor of EGFR, in incurable advanced cancers with EGFR exon 20 insertion (ex20ins) mutations.

TPS9155 Background: Oncogenic EGFR ex20ins mutations, found in ̃2% of non-small cell lung cancers (NSCLC) and a small percentage of other cancers, are generally not responsive to EGFR-targeted agents that have been approved for treatment of NSCLC with a common EGFR mutation, including L858R and exon 19 deletion. Similar to these more common types of EGFR-mutated NSCLC, CNS metastases are a challenge with EGFR ex20ins NSCLC and are associated with poor outcomes. While two EGFR ex20ins-targeting drugs were recently approved by the FDA (amivantamab and mobocertinib), neither have established CNS activity. BLU-451 is a CNS penetrant, wild type-sparing, covalent small molecule inhibitor of EGFR ex20ins as well as atypical (G719C, G719S, L861Q) and common EGFR mutants. Preclinical data have shown BLU-451 to have potent antitumor activity, including in an intracranial xenograft model, which has led to its clinical development in EGFR-mutant NSCLC. Methods: BLU-451-1101 (NCT05241873) is a phase 1/2, global, open-label study designed to evaluate single-agent BLU-451 in patients with NSCLC harboring EGFR ex20ins that has progressed following prior treatment for incurable recurrent or metastatic disease. Patients with Eastern Cooperative Oncology Group performance status 0–1 and EGFR ex20ins, exon 18 G719X or exon 21 L861Q mutant NSCLC (phases 1 and 2) or other cancers except primary CNS tumors (phase 1 only) are eligible. Patients with known ROS, RAF, ALK, or EGFR C797S mutations will be excluded. Stable, asymptomatic brain metastases are permitted, and active asymptomatic brain metastases are permitted in specific cohorts. Primary endpoints are determination of maximum tolerated dose (MTD), recommended phase 2 dose (RP2D), safety and tolerability (phase 1), in addition to evaluation of antitumor activity at the RP2D by RECIST v1.1 (phase 2). Secondary endpoints are evaluation of pharmacokinetics (PK) and antitumor activity by RECIST v1.1.(phase 1) and PK, safety, tolerability, and CNS antitumor activity (phase 2). Dose escalation will utilize a 3+3 design with up to 6 patients per cohort in phase 1 dose escalation and up to 12 per cohort in phase 1 dose expansion. Phase 2 will enroll patients in 3 cohorts (n = 18 each): patients with prior platinum-based chemotherapy and an EGFR ex20ins-targeted agent; patients with prior platinum but no EGFR ex20ins-targeted agent; and patients with active asymptomatic brain metastases with prior platinum with or without an EGFR ex20ins-targeted agent. The study is planned for approximately 40 centers in North America, the Asia-Pacific region, and/or Europe. Clinical trial information: NCT05241873.

HJM-561, a Potent, Selective, and Orally Bioavailable EGFR PROTAC that Overcomes Osimertinib-Resistant EGFR Triple Mutations.

The EGFR C797S mutation is the most common on-target resistance mechanism to osimertinib in patients with advanced non-small cell lung cancer (NSCLC). Currently there are no effective treatment options for patients with NSCLC harboring EGFR C797S triple mutants (Del19/T790M/C797S and L858R/T790M/C797S). Herein, we report an orally bioavailable EGFR PROTAC, HJM-561, which selectively degrades the EGFR C797S-containing triple mutants. HJM-561 potently inhibits the proliferation of Del19/T790M/C797S and L858R/T790M/C797S Ba/F3 cells while sparing cells expressing wild-type EGFR. Oral administration of HJM-561 shows robust antitumor activity in EGFR Del19/T790M/C797S-driven Ba/F3 CDX and PDX models that were resistant to osimertinib treatment. Taken together, our results suggest that HJM-561 is a promising therapeutic option for overcoming EGFR triple mutation-mediated drug resistance in NSCLC.

Triple positive lung cancer: A case report

Background: Targeted therapies in nonsmall cell lung cancer has changed the landscape of management and carved the disease in to more different sub types. Despite of considerable initial response to 1st generation and 2nd generation tyrosine kinase inhibitors patients develop resistance in the due course. Secondary mutations are due to threonine and methionine substitution at 790 (T790M) of EGFR. T790M mutation are resistant to 1st and 2nd generation TKI.Osimertinib is a irreversible third generation epidermal growth factor receptor tyrosine kinase inhibitor effective against EGFR T790M mutation positive lung cancer. Patients are inescapable of developing resistance with Osimertinib in spite of initial response and leaving no further definite therapeutic options. In 20-30% patients with osimertinib resistance develop EGFR C797S mutation. Our objective is to show the patient journey with primary, secondary mutation withT790M and tertiary mutation in C797S. Key Messages: Prospective molecular tumor profiling is now the standard of care in the treatment of metastatic NSCLC. Re-biopsy or liquid biopsy on progression of first and second line TKI to look for T790M has already been in routine practice. Re-biopsy or liquid biopsy on progression of third line TKI and molecular profiling can guide us in further management.

Investigating the genomic alteration improved the clinical outcome of aged patients with lung carcinoma

BackgroundLung carcinoma is a common geriatric disease. The development of genotype-targeted therapies greatly improved the management of lung carcinoma. However, the treatment for old patients can be more complex than that for young individuals.ResultsTo investigate the benefits of genetic detection for older patients with lung carcinoma, we explored the genomic profiling of 258 patients with more than 55 years using a targeted next generation sequencing, and some of these patients were treated with targeted therapies based on the results of genomic detection. KRAS codon 61 mutations were found in 15.2% KRAS-mutated patients, which tend to be co-existing with other classical activating mutations other than codons 12/13. Acquired EGFR C797S mutations were identified in 2 cases and ERBB2 amplification was identified in 1 case. All these 3 cases developed resistance to EGFR tyrosine kinase inhibitors and showed expected results of their followed therapies. The median progression-free survival and median overall survival of patients treated with molecular targeted therapies were better than those of patients treated with chemoradiotherapy alone.ConclusionsOur findings revealed the specific genomic profiles of patients older than 55 years with lung carcinoma and suggested that these old patients have been benefit from the genetic detection, which helped identify druggable mutations and distinguish resistance mechanisms.

Molecular landscape of osimertinib resistance in patients and patient-derived preclinical models.

Introduction:Osimertinib is a third-generation EGFR tyrosine kinase inhibitor (TKI) that is approved for the use of EGFR-mutant non-small cell lung cancer (NSCLC) patients. In this study, we investigated the acquired resistance mechanisms in NSCLC patients and patient-derived preclinical models.Methods:Formalin-fixed paraffin-embedded tumor samples and plasma samples from 55 NSCLC patients who were treated with osimertinib were collected at baseline and at progressive disease (PD). Next-generation sequencing was performed in tumor and plasma samples using a 600-gene hybrid capture panel designed by AstraZeneca. Osimertinib-resistant cell lines and patient-derived xenografts and cells were generated and whole exome sequencing and RNA sequencing were performed. In vitro experiments were performed to functionally study the acquired mutations identified.Results:A total of 55 patients and a total of 149 samples (57 tumor samples and 92 plasma samples) were analyzed, and among them 36 patients had matched pre- and post-treatment samples. EGFR C797S (14%) mutation was the most frequent EGFR-dependent mechanism identified in all available progression samples, followed by EGFR G824D (6%), V726M (3%), and V843I (3%). Matched pre- and post-treatment sample analysis revealed in-depth acquired mechanisms of resistance. EGFR C797S was still most frequent (11%) among EGFR-dependent mechanism, while among EGFR-independent mechanisms, PIK3CA, ALK, BRAF, EP300, KRAS, and RAF1 mutations were detected. Among Osimertinib-resistant cell lines and patient-derived models, we noted acquired mutations which were potentially targetable such as NRAS p.Q61K, in which resistance could be overcome with combination of osimertinib and trametinib. A patient-derived xenograft established from osimertinib-resistant patient revealed KRAS p.G12D mutation which could be overcome with combination of osimertinib, trametinib, and buparlisib.Conclusion:In this study, we explored the genetic profiles of osimertinib-resistant NSCLC patient samples using targeted deep sequencing. In vitro and in vivo models harboring osimertinib resistance revealed potential novel treatment strategies after osimertinib failure.

Molecular Characteristics of the Uncommon EGFR Exon 21 T854A Mutation and Response to Osimertinib in Patients With Non-Small Cell Lung Cancer

BackgroundEpidermal growth factor receptor (EGFR) T854A is an uncommon exon 21 mutation in patients with non-small cell lung cancer (NSCLC). It was first reported in samples collected after first generation EGFR tyrosine kinase inhibitor (TKI) treatment as an acquired resistant mutation to first generation EGFR-TKI. The efficacy of osimertinib, a third generation EGFR-TKI, in these patients was not clear. MethodsIn this study, a total of 8932 NSCLC patients with NGS data were retrospectively analyzed to investigate the molecular characteristics and clinical outcomes of patients with EGFR T854A mutation. ResultsEight of 8932 patients (0.09%) had EGFR T854A mutation, and 5 of them (62.5%) were treatment-naïve. Interestingly, all EGFR T854A mutations were co-occurred with EGFR L858R mutation in cis. TP53 was the most common concomitant mutation and no other driver mutation was found. Five of the 8 patients received treatment of osimertinib. Four patients achieved partial response, and one had stable disease, resulting in an overall objective response rate of 80% and disease control rate of 100%. The median progression-free survival of patients who received osimertinib was 10 months. Moreover, EGFR C797S mutation was detected in 1 patient after resistant to osimertinib treatment. ConclusionPresence of EGFR T854A mutation was rare in NSCLC patients and our retrospective study provides clinical evidence that osimertinib may be an effective treatment to improve survival outcomes in patients with EGFR T854A.

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.

Targeting BRAF Activation as Acquired Resistance Mechanism to EGFR Tyrosine Kinase Inhibitors in EGFR-Mutant Non-Small-Cell Lung Cancer.

Osimertinib has become a standard of care in the first-line treatment of advanced-stage non-small-cell lung cancer (NSCLC) harboring exon 19 and 21 activating mutations in the EGFR gene. Nevertheless, the 18.9-month median progression-free survival emphasizes the fact that resistance to osimertinib therapy is inevitable. Acquired resistance mechanisms to osimertinib in EGFR-driven NSCLC include MET amplification, EGFR C797S mutation, neuroendocrine differentiation, small-cell lung carcinoma histologic transformation, PD-L1 and KRAS amplifications and ESR1-AKAP12 and MKRN1-BRAF translocations, as well as BRAF V600 mutation. This last one represents 3% of the acquired resistance mechanisms to osimertinib. In this review, we discuss the rationale for EGFR/BRAF/MEK co-inhibition in the light of a clinical case of EGFR-mutant NSCLC developing a BRAF V600 mutation as an acquired resistance mechanism to osimertinib and responding to the association of osimertinib plus dabrafenib and trametinib. Additionally, we discuss the acquired resistance mechanisms to osimertinib plus dabrafenib and trametinib combination in that context.

Longitudinal Circulating Tumor DNA Analysis in Blood and Saliva for Prediction of Response to Osimertinib and Disease Progression in EGFR-Mutant Lung Adenocarcinoma.

Simple SummaryctDNA assay is a promising non-invasive method to detect genomic alterations associated with lung cancer. In this prospective study of 25 patients with EGFR-mutant lung adenocarcinoma receiving osimertinib, ctDNA progression predated radiographic progression by 118 days in 11 of 20 patients with disease progression. Saliva-based ctDNA analysis and plasma NGS detected additional patients with ctDNA progression preceding clinical progression, suggesting the potential complementary roles of different ctDNA detection methodologies. Baseline mutant ctDNA level predicted progression-free survival while tumor volume measurements by volumetric CT did not. Serial ctDNA analysis of plasma and saliva is a clinically useful tool to monitor response and resistance to osimertinib.Background: We assessed whether serial ctDNA monitoring of plasma and saliva predicts response and resistance to osimertinib in EGFR-mutant lung adenocarcinoma. Three ctDNA technologies—blood-based droplet-digital PCR (ddPCR), next-generation sequencing (NGS), and saliva-based EFIRM liquid biopsy (eLB)—were employed to investigate their complementary roles. Methods: Plasma and saliva samples were collected from patients enrolled in a prospective clinical trial of osimertinib and local ablative therapy upon progression (NCT02759835). Plasma was analyzed by ddPCR and NGS. Saliva was analyzed by eLB. Results: A total of 25 patients were included. We analyzed 534 samples by ddPCR (n = 25), 256 samples by NGS (n = 24) and 371 samples by eLB (n = 22). Among 20 patients who progressed, ctDNA progression predated RECIST 1.1 progression by a median of 118 days (range: 61–272 days) in 11 (55%) patients. Of nine patients without ctDNA progression by ddPCR, two patients had an increase in mutant EGFR by eLB and two patients were found to have ctDNA progression by NGS. Levels of ctDNA measured by ddPCR and NGS at early time points, but not volumetric tumor burden, were associated with PFS. EGFR/ERBB2/MET/KRAS amplifications, EGFR C797S, PIK3CA E545K, PTEN V9del, and CTNNB1 S45P were key resistance mechanisms identified by NGS. Conclusion: Serial assessment of ctDNA in plasma and saliva predicts response and resistance to osimertinib, with each assay having supplementary roles.

Abstract 1106: BRAF and EGFR fusion as a novel mechanism of resistance mechanism to Lazertinib, 3rd- generation EGFR-TKI, in EGFR-mutant NSCLC

Abstract Background: EGFR-TKI is an established first-line therapy for NSCLC with activating EGFR mutations. Osimertinib, third-generation EGFR TKI, was investigated as a first-in-class drug, but lazertinib(YH25448) was also reported as an outstanding drug which had similar efficacy as osimertinib. Nevertheless, acquired resistance is inevitably developed by third-generation EGFR-TKIs in clinic. Even though EGFR C797S mutation has been identified as a major resistant mechanism, the remaining resistance mechanisms to these TKIs are largely unknown. Methods: To explore the mechanism of resistance to lazertinib, we firstly established drug-resistant cells to lazertinib in vitro using four NSCLC cells including the patient-derived cell line (PDC), patient-derived tumor xenograft cell line (PDTC), and ATCC cell lines. To analyze the changes in global genetic alterations and gene expression of established lazertinib-resistant cell lines(YH1R), whole exome sequencing (WES) and RNA sequencing (RNA-seq) were performed. The effect of EGFR/BRAF fusion was investigated in vitro using established YH1R cell line and various patient-derived tumor xenograft samples. Western blot study was used to investigate EGFR and MAPK cascade signaling pathway. We evaluated antitumor activity of MEK inhibitor and lazertinib combination treatment in lazertinib-resistant NSCLC cells with EGFR/BRAF fusion in vitro and in vivo. Results: RNA-seq data revealed a novel EGFR/BRAF fusion transcript (EGFR Exon 19-BRAF Exon 9, in-frame fusion) in lazertinib-resistant PC9GR_YH1R. The fusion gene consisted of EGFR (Exon 1-19) portion and BRAF kinase domain (Exon 9-18). The EGFR/BRAF fusion mRNA and protein were specifically upregulated in PC9GR_YH1R compared to parental cells. Intriguingly, we detected the EGFR/BRAF fusion gene expression in patient-derived xenografts (YHIM-1045 and YHIM-1035) obtained from patients who experienced acquired resistance to lazertinib. Compared with treatment with either single agent, combination treatment of lazertinib and MEK inhibitor, trametinib or selumetinib, was significantly effective at inhibiting cell proliferation as well as EGFR signaling pathways in PC9GR_YH1R in vitro and in vivo. Conclusion: We found a novel EGFR/BRAF fusion gene, as a key driver of acquired resistant mechanism of lazertinib, in NSCLC cell lines and patient-derived xenografts with acquired resistance to lazertinib. Combination treatment of lazertinib and MEK inhibitor showed a strong antitumor effect in lazertinib-acquired resistant NSCLCs, indicating that the combination therapy of EGFR and MEK inhibitors might be a promising therapeutic option for overcoming lazertinib-acquired resistant NSCLC patients in clinic. Citation Format: Seo-Yoon Jeong, Jiyeon Yun, San-Duk Yang, Soo-Hwan Lee, Sangbin Lim, Seok-Young Kim, Min Hee Hong, Sun Min Lim, Hye Ryun Kim, Hye Ryun Kim, Byoung Chul Cho. BRAF and EGFR fusion as a novel mechanism of resistance mechanism to Lazertinib, 3rd- generation EGFR-TKI, in EGFR-mutant NSCLC [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 1106.

Comparison of Resistance Spectra after First and Second Line Osimertinib Treatment Detected by Liquid Biopsy.

Simple SummarySince the recent approval of osimertinib, a third generation tyrosine kinase inhibitor (TKI) targeting EGFR in non-small cell lung cancer (NSCLC), tracing the resistance mechanisms that yield to failure of osimertinib has become of interest. As the spectrum of osimertinib-resistance related genomic alterations appears significantly more diverse compared to first and second generation TKI, comprehensive, and preferably non-invasive molecular diagnostic methods are required for the detection of resistance mechanisms. In this study, we present molecular results of 56 NSCLC patients during disease progression on first and second line osimertinib treatment using a hybrid capture (HC) next generation sequencing (NGS) based liquid biopsy approach. We show examples of polyclonal resistance development which leads to the presence of multiple resistance mechanisms in the same patient, and highlight the clinical utility of HC NGS over single gene testing.Since 2009, several first, second, and third generation EGFR tyrosine kinase inhibitors (TKI) have been approved for targeted treatment of EGFR mutated metastatic non-small lung cancer (NSCLC). A vast majority of patients is improving quickly on treatment; however, resistance is inevitable and typically occurs after one year for TKI of the first and second generation. Osimertinib, a third generation TKI, has recently been approved for first line treatment in the palliative setting and is expected to become approved for the adjuvant setting as well. Progression-free survival (PFS) under osimertinib is superior to its predecessors but its spectrum of resistance alterations appears significantly more diverse compared to first and second generation EGFR TKI. As resistance mechanisms to osimertinib are therapeutically targetable in some cases, it is important to comprehensively test for molecular alterations in the relapse scenario. Liquid biopsy may be advantageous over tissue analysis as it has the potential to represent tumor heterogeneity and clonal diversification. We have previously shown high concordance of hybrid capture (HC) based next generation sequencing (NGS) in liquid biopsy versus solid tumor biopsies. In this study, we now present real-word data from 56 patients with metastatic NSCLC that were tested by liquid biopsy at the time of disease progression on mostly second line treated osimertinib treatment. We present examples of single and multiple TKI resistance mechanisms, including mutations in multiple pathways, copy number changes and rare fusions of RET, ALK, FGFR3 and BRAF. In addition, we present the added value of HC based NGS to reveal polyclonal resistance development at the DNA level encoding multiple EGFR C797S and PIK3CA mutations.

Primary and secondary resistance mechanisms in first, second and third generation tyrosine kinase inhibitors in EGFR mutant non-small cell lung cancer patients.

e21142 Background: Different molecular mechanisms of on target and off target primary and secondary resistance have been observed in EGFR mutant NSCLC patients after first(1st), second(2nd) and third (3rd) generation of tyrosine kinase inhibitors(TKIs). Next generation sequencing(NGS) offers a comprehensive method of detecting these mechanisms to decide next line of treatment. Methods: We retrospectively analyzed 430 samples of NSCLC for primary and secondary resistance to 1st, 2nd and 3rd TKIs. NGS was performed using thermofischer Ion Torrent Oncomine Focus 52 gene Assay. These cases were divided into 4 groups.1)Primary resistance to first and second generation TKIs 2)Primary resistance to 3rd generation TKI 3)Secondary resistance to 1st and 2nd generation TKI 4) Secondary resistance to 3rd generation TKI.Last group was further subgrouped into A when 3rd generation TKI was offered as second line after 1st or 2nd generation TKIs on detection of T790M and subgroup B when it was given as first line. Results: Group1 had 13 cases. There were 2 cases of complex EGFR exon 19 mutation p.Glu746_Leu747delinsValPro, 4 cases of EGFR exon 20 insertion, 1 case of dual EGFR L833V & H835L mutation, 2 cases with EGFR amplification with EGFR exon 19 del and PIK3CA C420_P421del along with EGFR exon 19 del. Four cases had no additional abnormality. Group 2 had 5 cases:1 case had L858R and E709A dual mutation, 2 cases had KRAS G13C and KRAS G12V along with EGFR exon 19 del. One case had EGFR amplification and one case had MET amplification along with EGFR exon 19 del respectively.Group 3 had 34 cases including 10 cases of EGFR L858R and 24 cases of exon 19 deletion.T790M mutation was detected in 8 patients, MET amplification in 7 cases,one case had both T790M and MET amplification. One case lost the primary EGFR exon 19 del. Others mutations detected were KRAS G13C, PIK3CA H1047R, TP53 R213Q and TP53 C242fs. Group3 had 15 cases with 7 cases in subgroup A and 9 cases in subgroup B. In subgroup A T790M mutation was lost in 6 out of 7 cases.One case which lost T790M developed ALK translocation.One case of EGFR exon 19 del retained EGFR T790M with EGFR C797S in cis allele. Other mutations detected were PIK3CA E542K and KRAS G12C. In subgroup B one case showed EGFR C797S(both cis and trans) besides the primary EGFR exon 19 del. One case showed BRAF G469A along with EGFR exon 19 del. Other mutations detected were CTNNB1 D32N, KRAS G12V, and PIK3CA E542K. Conclusions: Primary and secondary acquired resistance is unavoidable in EGFR mutant advanced NSCLC on any generation of TKIs. NGS offers an advantage in diagnosing mechanism of resistance for further choice of therapy.

Efficacy and safety of patritumab deruxtecan (HER3-DXd) in EGFR inhibitor-resistant, EGFR-mutated (EGFRm) non-small cell lung cancer (NSCLC).

9007 Background: Patients (pts) with advanced EGFRm NSCLC have limited treatment options after failure of EGFR TKI and platinum-based chemotherapy (PBC). HER3-DXd is an antibody drug conjugate consisting of a fully human monoclonal antibody to HER3 attached to a topoisomerase I inhibitor payload via a tetrapeptide-based cleavable linker. We previously presented efficacy/safety data (median follow-up, 5.4 mo) from an ongoing study of HER3-DXd in EGFRm NSCLC after failure of EGFR TKI therapy. We now present extended follow-up of pts receiving the recommended dose for expansion (5.6 mg/kg IV Q3W). Methods: This Ph 1 dose-escalation/expansion study included pts with locally advanced or metastatic EGFRm NSCLC with prior EGFR TKI therapy (NCT03260491). Pts with stable brain metastases (BM) were allowed. The primary endpoint was confirmed ORR by blinded independent central review (BICR) per RECIST v1.1; secondary endpoints included DOR, PFS and safety. Results: At data cutoff (Sept 24, 2020), 57 pts were treated with HER3-DXd 5.6 mg/kg IV Q3W; median follow-up, 10.2 mo (range, 5.2-19.9 mo). Median number of prior anticancer regimens was 4 (range, 1-10). 100% had prior EGFR TKI (86% prior osimertinib [OSI]) and 91% had prior PBC. 47% had a history of BM. Median treatment duration was 5.5 mo (range, 0.7-18.6 mo); treatment was ongoing in 18 pts (32%). Confirmed ORR by BICR was 39% (22/57; 95% CI, 26.0%-52.4%; 1 CR, 21 PR, 19 SD) with 14/22 responses occurring within 3 mo of starting HER3-DXd. DCR was 72% (95% CI, 58.5%-83.0%). Median DOR was 6.9 mo (95% CI, 3.1 mo-NE), and median PFS was 8.2 mo (95% CI, 4.4-8.3 mo). Antitumor activity was observed across diverse mechanisms of EGFR TKI resistance, including those not directly related to HER3 ( EGFR C797S, MET or HER2 amp, and BRAF fusion). Among pts with prior PBC, ORR was 37% (19/52; 95% CI, 23.6%-51.0%); in pts with prior OSI and PBC, ORR was 39% (17/44; 95% CI, 24.4%-54.5%). Among 43 pts evaluable for HER3 expression, nearly all expressed HER3; median membrane H-score by IHC was 180 (range, 2-280). Median H-score (range; N) was 195 (92-268; 15) in pts with CR/PR, 180 (4-280; 15) with SD, 126.5 (2-251; 6) with PD, and 180 (36-180; 7) in pts unevaluable for best overall response. The most common grade ≥3 adverse events (AEs) were thrombocytopenia (30%), neutropenia (19%), and fatigue (14%). Drug-related interstitial lung disease by central adjudication occurred in 4 pts (7%; 1 grade ≥3 [2%]; no grade 5). 6/57 pts (11%) had AEs associated with treatment discontinuation (none were due to thrombocytopenia). Conclusions: HER3-DXd 5.6 mg/kg IV Q3W demonstrated antitumor activity across various EGFR TKI resistance mechanisms in heavily pretreated metastatic/locally advanced EGFRm NSCLC. The safety profile was consistent with previous reports. A Ph 2 study of HER3-DXd in pts with EGFRm NSCLC after failure of EGFR TKI and PBC has been initiated (NCT04619004). Clinical trial information: NCT03260491.

Incidence and heterogeneity of C797S and other EGFR resistance mutations on routine comprehensive genomic profiling (CGP).

9101 Background: The emergence of osimertinib (osi) as standard of care therapy for EGFR-mutant NSCLC has led to investigations into understanding and overcoming drug resistance. There are now a number of therapeutic approaches aimed at overcoming EGFR resistance mutations (muts). We sought to understand the biology of EGFR C797S and other EGFR resistance muts through querying our clinico-genomic database (CGDB). Methods: CGP results from tissue (n = 60,889) or circulating tumor DNA (ctDNA; [n = 9,922]) samples from 70,811 NSCLC patients (pts) were queried for known osi resistance muts in EGFR (C797, L792, G796, L718, G724). Clinical outcomes were evaluated for a cohort of NSCLC pts with osi resistance from the Flatiron Health-Foundation Medicine CGDB, a nationwide de-identified EHR-derived database linked to CGP data. Results: Between 12/2014 and 11/2020, 261 osi resistance mutations in EGFR were detected in 228 samples. The most common were C797S (66%), L718X (14%), G724S (11%), and others (9%). 173 C797S muts were detected in 155 samples (123 ex19del, 30 L858R, 2 other EGFR muts); 100 tissue, 55 ctDNA (median VAF = 7.6%). EGFR T790M co-occurred with C797S muts (96% cis, 3.7% trans) in 118 (76%) samples and decreased over time, occurring in 92% (24/26) of C797S samples tested in 2017 vs 56% (20/36) of samples tested in 2020 (p = 0.002). In 19/155 (12%) samples with C797S (14 ctDNA), multiple changes resulting in EGFR resistance muts were present: 16 samples had > 1 nucleotide changes resulting in C797S (100% trans), 3 samples had other resistance muts (L718Q/V, L792H, L792F) and 3 samples had multiple C797S changes with other resistance muts (C797G, L792H/F + G796S, L718Q + G796S+C797G). 29 pts (14 ctDNA) had C797S with potential off-target resistance (17 PIK3CA muts, 4 BRAF muts, 3 CCDC6- RET fusions, 3 KRAS muts, 2 ERBB2 amplifications (amps), 1 ERBB2 ex16 del, 1 STRN- ALK fusion, 1 FGFR3- TACC3 fusion). In the CGDB, 527 EGFR-mut NSCLC pts had documented receipt of osi. Pre and post osi-treated specimens were available for 19 of these pts (12 ex19del, 6 L858R, 1 G719A/S768I). Heterogeneous acquired resistance mechanisms were observed in the post-osi specimen, including 2 CCDC6- RET fusions, 2 MET amps, 2 BRAF fusions, BRAF V600E, and secondary EGFR muts (C797S, L704F, L718V). 161/527 pts had a documented line of therapy after osi discontinuation and most frequently received platinum doublet + immunotherapy (27%) or platinum doublet alone (23%); 17 (11%) pts received another EGFR tyrosine kinase inhibitor. 214/527 had documented osi progression and median post-progression survival was 11.8 months. Conclusions: Osi resistance in EGFR-mutant NSCLC is a poor prognosis condition. EGFR C797S is a recurring resistance mut which, in a minority of cases, can co-occur with alternate on and off target resistance muts detected with tissue and liquid biopsy.

Molecular characteristics of EGFR exon 20 uncommon R776H mutation and response to osimertinib in NSCLC patients.

e21001 Background: EGFR R776H is an uncommon exon 20 mutation in non-small cell lung cancer (NSCLC) patients. This mutation was first reported in samples after first generation EGFR TKI treatment as an acquired resistant mutation to first generation of EGFR-TKI. We further analyzed the molecular characteristics of patients with EGFR R776H mutation and its correlation with EGFR TKI therapy. Methods: In this study, a total of 16131 NSCLC patients from multiple centers with NGS data were retrospectively analyzed to study the molecular characteristics and clinical outcomes of patients with EGFR R776H mutation. Results: 44 of the 16131 patients (0.27%) had EGFR R776H mutation, and 28 of them (63.6%) were treatment-naïve while performing the mutation test. TP53 was the most common concomitant mutation in both treatment-naïve (57.1%) and treated (81.3%) patients. EGFR R776H mutation was found to coexist with multiple types EGFR mutation. The common mutations were EGFR L858R (54%) and EGFR G719A/S (25%), but It almost never coexists with 19del (2%). The coexist of EGFR R776H mutation was similar in both treatment-naïve and treated patients. In 16 of treated patients, all had received first - or second-generation EGFR TKI treatment, and the median progression-free survival (PFS) was 9 months. Interestingly, four of them found the presence of not only EGFR R776H but also EGFR T790M. It may be that EGFR R776H and T790M appear together in drug resistance, or it may be that EGFR R776H and EGFR sensitive mutation are not in the same cell clone. Two patients with EGFR R776H received treatment of Osimertinib and achieved partial response. The PFS of two patients in Osimertinib were 11 and 10 months, respectively. Moreover, EGFR C797S mutation was detected in two patients after resistant to Osimertinib. Conclusions: Presence of EGFR R776H mutation was rare in NSCLC patients and our retrospective study provides clinical evidence that Osimertinib could be of benefit and may potentially be an effective treatment strategy to improve survival outcomes in patients with EGFR R776H.

The value of defining molecular resistance in patients with progressive EGFR and ALK-driven lung cancer in a public system.

3126 Background: Repeat molecular profiling, except to detect EGFR T790M, is not routinely performed in Canadian patients with lung cancer progressing on EGFR tyrosine kinase inhibitors (TKIs). We performed genomic profiling on post-progression biopsies in patients with stage IV non-small cell lung cancer (NSCLC) and known EGFR/ ALK aberrations treated with TKIs to identify resistance mechanisms, evaluate options for subsequent treatment, and to assess clinical trial eligibility and costs. Methods: From Feb 2018-Aug 2020, post-progression tumour biopsies from consenting patients at a major cancer centre underwent genomic profiling (ThermoFisher OCA v3.0 including hotspots, fusions, and copy number variations in 161 cancer-associated genes). Outcomes of interest were the identification of resistance mutations, actionable targets, clinical trial eligibility (per clinicaltrials.gov), and costs. Results: Thirty-two patients consented to the study. Most, 84% (n = 27), had successful testing completed while 16% (n = 5) had insufficient tissue. Median age of the cohort was 56 yrs, 59% (n = 16) were female, 74% (n = 20) were never-smokers, 81% (n = 22) had ECOG performance status 0-1, and 67% (n = 18) were Asian. The majority, 81% (n = 22) had EGFR mutated NSCLC, and had progressed on EGFR TKIs (15 with previously identified T790M had progressed on osimertinib), and 19% (n = 5) had ALK fusions. Patients had received a median of 2 prior lines of targeted therapy prior to re-biopsy (IQR 1.5,3). One patient had evidence of small cell transformation and associated TP53 and RB1 mutations, 11% (n = 3) had acquired EGFR C797S mutations, and 11% (n = 3) had acquired ALK resistance point mutations (G1202R n = 2, I1171N n = 1). Genomic profiling identified additional actionable targets in 19% of patients (n = 5: MET exon 14 skip mutation n = 1, MET amplification n = 2, BRAF V600E n = 2). Overall, 33% (n = 9) patients had management-changing resistance mechanisms identified (small cell transformation n = 1, actionable targets n = 5, ALK inhibitor resistance = 3). New clinical trial options based on genomic profiling results were identified for 67% (n = 18) of patients. Incremental costs for repeat genomic profiling were approximately $880 CAD per case. Conclusions: Molecular profiling upon development of resistance to targeted therapy in our cohort revealed actionable resistance mechanisms for over a third of patients and clinical trial options for 67%. These incremental benefits for patients highlight the importance of routine molecular profiling in the setting of acquired TKI resistance in lung cancer.

Monitoring epidermal growth factor receptor C797S mutation in Japanese non-small cell lung cancer patients with serial cell-free DNA evaluation using digital droplet PCR.

Osimertinib is a third‐generation epidermal growth factor receptor tyrosine kinase inhibitor (EGFR‐TKI) that is effective in treating both naïve and T790M‐mutated EGFR‐TKI‐resistant non–small cell lung cancer patients. The EGFR C797S mutation is the major osimertinib resistance mechanism. The present study monitored the EGFR C797S mutation during osimertinib treatment in Japanese patients using droplet digital PCR (ddPCR). In our first cohort, C797S detection was validated with tumor specimens and/or plasma samples from 26 patients using ddPCR with custom‐designed probes detecting and discriminating T790M and C797S in cis and trans positions. In our second cohort, 18 patients with EGFR‐T790M who were going to start osimertinib were analyzed using ddPCR by collecting the plasma samples every month from the beginning of the course of osimertinib. In the first cohort, C797S was detected in 15.4% of patients. C797S and T790M in cis and trans positions were distinguished using ddPCR. In the second cohort, serial cfDNA evaluation revealed that the rate of EGFR mutation changes with disease state. Increases of EGFR mutation were detected, including C797S several months before the diagnosis of disease progression. As with the first cohort, C797S and T790M in cis and trans position were distinguished by ddPCR at disease progression. Coincidentally, in the first cohort, next generation sequencing detected NRAS Q61K mutation and the resistance with NRAS Q61K mutation was overcome by trametinib. In the second cohort, serial cfDNA analysis was useful for evaluating bone oligo‐progression and local radiation therapy.

Dynamic cfDNA Analysis by NGS in EGFR T790M-Positive Advanced NSCLC Patients Failed to the First-Generation EGFR-TKIs.

PurposeCirculating cell-free DNA (cfDNA) level has been demonstrated to be associated with efficacy in first generation EGFR TKIs in non-small cell lung cancer (NSCLC). However, the role of dynamic cfDNA analysis using next-generation sequencing (NGS) in patients with subsequent third-generation EGFR TKIs remains unclear.MethodsFrom 2016 to 2019, 81 NSCLC patients with EGFR T790M mutation either in tissue or plasma who received third-generation EGFR TKIs treatment were enrolled. CfDNA were sequenced by NGS with a 425-gene panel. The association of clinical characteristics, pretreatment, dynamic cfDNA and T790M level with outcomes in patients treated with the third-generation TKIs were analyzed.ResultsIn univariate analysis, the median PFS of patients with undetectable cfDNA level during treatment was significantly longer than those with detectable cfDNA (16.97 vs. 6.10 months; HR 0.2109; P < 0.0001). The median PFS of patients with undetectable T790M level during treatment was significantly longer than those with detectable T790M (14.1 vs. 4.4 months; HR 0.2192; P < 0.001). Cox hazard proportion model showed that cfDNA clearance was an independent predictor for longer PFS (HR 0.3085; P < 0.001) and longer OS (HR 0.499; P = 0.034). The most common resistant mutations of the third-generation TKIs were EGFR C797S (24%). CDK6 CNV, GRIN2A, BRCA2, EGFR D761N, EGFR Q791H, EGFR V843I, and ERBB4 mutation genes may possibly be new resistant mechanisms.ConclusionsPatients with undetectable cfDNA during the third-generation EGFR TKI treatment have superior clinical outcomes, and dynamic cfDNA analysis by NGS is valuable to explore potential resistant mechanisms.

Novel Resistance Mechanisms to Osimertinib Analysed by Whole-Exome Sequencing in Non-Small Cell Lung Cancer

PurposeMolecular-based targeted therapy has improved life expectancy for advanced non-small cell lung cancer (NSCLC). However, it does not have to be inevitable that patients receiving third-generation EGFR-TKIs become drug resistant. EGFR C797S and MET amplification are common mechanisms of osimertinib. However, a large part of these potential drug mechanisms remains unknown, and further research is needed.MethodsTumour and blood samples from forty advanced NSCLC patients were identified as acquired drug resistant to osimertinib. The NGS panel was applied to detect EGFR C797S and MET amplification in tumour tissues or plasma samples. Whole-exome sequencing was conducted in five pairs of tumour tissues obtained before osimertinib administration and after osimertinib resistance in patients without C797S/cMET amplification.ResultsThe overall C797S mutation rate was 20%, and MET amplification was detected in six out of sixteen C797S-negative samples. PDGFRA in the PI3K-AKT-mTOR signalling pathway, RASAL2, RIN3 and SOS2 in the RAS-Raf-ERK signalling pathway, PTK2 in the ERBB signalling pathway and ABCC1 and ABCB5 in the ABC membrane pump system were identified as candidate crucial genes of drug resistance to osimertinib.ConclusionEGFR C797S mutation and MET amplification are leading mechanisms for osimertinib resistance in lung cancer. The crucial potential mutated genes defined in our present study may need further validation in a considerable number of lung cancer patients.

Integrating Liquid Biopsy and Radiomics to Monitor Clonal Heterogeneity of EGFR-Positive Non-Small Cell Lung Cancer

BackgroundEGFR-positive Non-small Cell Lung Cancer (NSCLC) is a dynamic entity and tumor progression and resistance to tyrosine kinase inhibitors (TKIs) arise from the accumulation, over time and across different disease sites, of subclonal genetic mutations. For instance, the occurrence of EGFR T790M is associated with resistance to gefitinib, erlotinib, and afatinib, while EGFR C797S causes osimertinib to lose activity. Sensitive technologies as radiomics and liquid biopsy have great potential to monitor tumor heterogeneity since they are both minimally invasive, easy to perform, and can be repeated over patient’s follow-up, enabling the extraction of valuable information. Yet, to date, there are no reported cases associating liquid biopsy and radiomics during treatment.Case presentationIn this case series, seven patients with metastatic EGFR-positive NSCLC have been monitored during target therapy. Plasma-derived cell free DNA (cfDNA) was analyzed by a digital droplet PCR (ddPCR), while radiomic analyses were performed using the validated LifeX® software on computed tomography (CT)-images. The dynamics of EGFR mutations in cfDNA was compared with that of radiomic features. Then, for each EGFR mutation, a radiomic signature was defines as the sum of the most predictive features, weighted by their corresponding regression coefficients for the least absolute shrinkage and selection operator (LASSO) model. The receiver operating characteristic (ROC) curves were computed to estimate their diagnostic performance. The signatures achieved promising performance on predicting the presence of EGFR mutations (R2 = 0.447, p <0.001 EGFR activating mutations R2 = 0.301, p = 0.003 for T790M; and R2 = 0.354, p = 0.001 for activating plus resistance mutations), confirmed by ROC analysis.ConclusionTo our knowledge, these are the first cases to highlight a potentially promising strategy to detect clonal heterogeneity and ultimately identify patients at risk of progression during treatment. Together, radiomics and liquid biopsy could detect the appearance of new mutations and therefore suggest new therapeutic management.