SCLC Transformation Research Articles

P1.03G.02 Genotyping of RB1 Status Identifies Two Distinct Subtypes in EGFR-Mutant Lung Cancers with SCLC Transformation

P1.03G.02 Genotyping of RB1 Status Identifies Two Distinct Subtypes in EGFR-Mutant Lung Cancers with SCLC Transformation

Combination of Cytologic Findings and Circulating Tumor DNA From Cerebrospinal Fluid Revealed SCLC Transformation in Patients With Leptomeningeal Metastases of Lung Adenocarcinoma

IntroductionTransformation to SCLC is a resistance mechanism to tyrosine kinase inhibitor in EGFR-mutated lung adenocarcinoma (LUAD). Nevertheless, the clinical and molecular features of SCLC transformation in LUAD with leptomeningeal metastases (LM) are scarce. MethodsWe retrospectively collected 237 patients with NSCLC who underwent lumbar puncture owing to suggestion of LM. All SCLC transformation in cerebrospinal fluid (CSF) was confirmed by two experienced pathologists using cytologic evaluation. CSF circulating tumor DNA (ctDNA) was tested by next-generation sequencing. ResultsTumor cells in CSF samples were found in 111 patients (111 of 237, 46.8%), and eight cases (eight of 111, 7.2%) were identified as having SCLC cells in CSF. Seven patients carried the EGFR mutation, including four patients with EGFR exon 19 deletion and three patients with EGFRexon21 L858R mutation. Another patient harbored ERBB2 insertion. Seven of these patients were resistant to targeted therapy. CSF ctDNA analysis reported that TP53 and RB1 mutations were common. The median time from the diagnosis of advanced NSCLC to SCLC transformation found in CSF was 9.7 months (95% confidence interval [CI]: 4.0–17.5 mo). The median overall survival since the initial diagnosis of metastatic NSCLC was 15.3 months (95% CI: 1.2–29.4 mo). The median overall survival after SCLC transformation detected in CSF was 5.0 months (95% CI: 4.0–5.9 mo). ConclusionsSCLC transformation may be revealed in CSF by both cytologic evaluation and ctDNA, not just in tissue that underwent rebiopsy. SCLC transformation of CSF is informative for resistance mechanism in patients with LUAD with LM on tyrosine kinase inhibitor progression, which was associated with poor survival.

Genomic landscape of MTAP deletions and association with EGFR alterations in NSCLC.

8599 Background: Genomic loss of 9p21, containing methylthioadenosine phosphorylase ( MTAP) and CDKN2A/B,is frequently observed across cancers, including non-small cell lung cancer (NSCLC). With the clinical development of multiple classes of agents aimed at achieving synthetic lethality in the context of MTAP deletions (del) across solid tumors, including novel PRMT5 and MAT2A inhibitors, there is a need to understand the genomic landscape and outcomes of patients with NSCLC and MTAP del. Methods: All NSCLC samples sequenced with MSK-IMPACT v7, a DNA-based NGS panel with coverage for 505 genes including MTAP and CDKN2A/B were queried. MTAP-del and CDKN2A-del were defined by significantly low read counts in coverage-based copy number analyses. Analyses of enrichment in co-altered genes between MTAP-del and MTAP-intact tumors were completed using Fisher tests with multiple test correction. For subsequent analyses, samples profiled with earlier MSK-IMPACT versions not covering MTAP were manually reviewed for 9p21 status. Results: Of 3010 NSCLC samples sequenced, 246 (8.2%) had MTAP del; of these, 243/246 (99%) had concurrent CDKN2A del. Among MTAP-del compared to MTAP-intact tumors, EGFR ( Q = 0.01) and SMARCA2 ( Q < 0.01) alterations were more frequent, while KRAS ( Q = 0.05) and RB1 ( Q = 0.02) alterations were less frequent. Patients (pts) with MTAP-del tumors were more likely to be Asian ( P < 0.01) and never smokers ( P < 0.01). We next identified 193 pts with stage IV MTAP-del lung adenocarcinoma (LUAD). Among these pts, 121/193 (63%) had concurrent oncogenic driver alterations with approved first-line targeted therapies, including 46% with EGFR sensitizing alterations (26% EGFR exon 19 del, 17% EGFR L858R). Among pts with advanced EGFR exon 19 del or L858Rlung cancer treated with 1L osimertinib (osi), MTAP-del was not associated with significant differences in time to discontinuation (TTD) of osi (median TTD 19 months vs 24 months for MTAP-intact, HR = 1.2, P = 0.57). We then identified 69 pts with paired NGS available pre- and post-progression on osi who were MTAP-intact at baseline. Acquired MTAP del was found in 10/69 (14%) of these pts at progression on osi, which was more frequent than any previously characterized osi acquired resistance (AR) mechanism (SCLC transformation: 13%, EGFR amplification [amp]: 10%, MET amp: 10%, EGFR C797S: 7%). In 4 of these pts, acquired MTAP del was seen in the absence of other AR mechanisms, while in 6 pts, acquired MTAP del was seen alongside an additional mechanism ( EGFR amp: 2, EGFR C797S: 1, EGFR L718Q: 1, SCLC transformation: 1, MET amp: 1). Conclusions: Among pts with advanced LUAD, MTAP deletions are enriched in tumors with targetable driver alterations, particularly in EGFR, and are frequently observed at acquired resistance to osimertinib. Demonstration of activity of novel agents targeting MTAP deficiency could be of significant benefit to pts with EGFR-and other oncogene-driven lung cancers.

Abstract LB453: Distinct mechanism of CXCR7 activation in EGFR-mutated NSCLC by chemokines

Abstract Erlotinib and gefitinib, EGFR TKIs, have markedly improved outcomes for NSCLC patients with EGFR mutations. However, resistance eventually develops, with the T790M mutation evident in over 50% of resistant tumors. Other resistance pathways include MET amplification, SCLC transformation, and EMT. Osimertinib, a third-generation EGFR TKI, targets the T790M mutation and is approved as a first-line treatment, reducing the incidence of T790M-related resistance. Nonetheless, non-T790M resistance mechanisms such as mesenchymal transformation are on the rise. The molecular targets or exact mechanisms of EGFR TKI resistance with mesenchymal phenotypes remain elusive. We have discovered that ERK reactivation, commonly found in EGFR TKI-resistant cells with a mesenchymal phenotype, is due to activation of an atypical GPCR, CXC chemokine receptor type 7 (CXCR7). CXCR7 is overexpressed in a cell line, an EGFR TKI-resistant tumor model, and in samples from patients that progressed on EGFR TKIs. Currently, there are no effective CXCR7 inhibitors to evaluate in NSCLC; the mechanisms and ligands for CXCR7 are not fully understood. To evaluate ligand-dependent activation of CXCR7, we generated HEK293 cells and EGFR-mutant NSCLC cells ectopically-expressing CXCR7 and stimulated the cells with CXCL12, a well-documented ligand for CXCR7. Exposures of HEK293 cells with CXCR7 to CXCL12 resulted in the internalization of CXCR7 followed by the activation of the MAPK pathway within 30 minutes of EGFR TKI treatment whereas MAPK activation in EGFR mutant NSCLC cells took 8 hours. MIF activation was also delayed in NSCLC compared to the HEK293 model, requiring the presence of an EGFR TKI. We discovered that CXCR7 co-immunoprecipitated with mutant EGFR in NSCLC cells while CXCR7 did not co-immunoprecipitate when EGFR was inhibited. Furthermore, we discovered additional chemokines including GDF15 that activate the CXCR7-MAPK axis and promote cell migration, a key characteristic of the mesenchymal phenotype in EGFR mutant cells. Taken together, we elucidated a unique mechanism of ligand-induced activation of CXCR7 and downstream MAPK pathway by canonical and putative ligands. This complex mechanism of CXCR7 activation in EGFR mutant NSCLC suggests that preventing the receptor-ligand binding may not be feasible in the context of overcoming EGFR TKI resistance. Citation Format: Laura C. Gunder, Ines Pulido, Jeffrey H. Becker, Malek G. Massad, Takeshi Shimamura. Distinct mechanism of CXCR7 activation in EGFR-mutated NSCLC by chemokines [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 2 (Late-Breaking, Clinical Trial, and Invited Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(7_Suppl):Abstract nr LB453.

Brief Report: Comprehensive Clinicogenomic Profiling of Small Cell Transformation From EGFR-Mutant NSCLC Informs Potential Therapeutic Targets

IntroductionNSCLC transformation to SCLC has been best characterized with EGFR-mutant NSCLC, with emerging case reports seen in ALK, RET, and KRAS-altered NSCLC. Previous reports revealed transformed SCLC from EGFR-mutant NSCLC portends very poor prognosis and lack effective treatment. Genomic analyses revealed TP53 and RB1 loss of function increase the risk of SCLC transformation. Little has been reported on the detailed clinicogenomic characteristics and potential therapeutic targets for this patient population. MethodsIn this study, we conducted a single-center retrospective analysis of clinical and genomic characteristics of patients with EGFR-mutant NSCLC transformed to SCLC. Demographic data, treatment course, and clinical molecular testing reports were extracted from electronic medical records. Kaplan-Meier analyses were used to estimate survival outcomes. Next generation sequencing-based assays was used to identify EGFR and co-occurring genetic alterations in tissue or plasma before and after SCLC transformation. Single-cell RNA sequencing (scRNA-seq) was performed on a patient-derived-xenograft model generated from a patient with EGFR-NSCLC transformed SCLC tumor. ResultsA total of 34 patients were identified in our study. Median age at initial diagnosis was 58, and median time to SCLC transformation was 24.2 months. 68% were female and 82% were never smokers. 79% of patients were diagnosed as stage IV disease, and over half had brain metastases at baseline. Median overall survival of the entire cohort was 38.3 months from initial diagnoses and 12.4 months from time of SCLC transformation. Most patients harbored EGFR exon19 deletions as opposed to exon21 L858R alteration. Continuing EGFR tyrosine kinase inhibitor post-transformation did not improve overall survival compared with those patients where tyrosine kinase inhibitor was stopped in our cohort. In the 20 paired pretransformed and post-transformed patient samples, statistically significant enrichment was seen with PIK3CA alterations (p = 0.04) post-transformation. Profiling of longitudinal liquid biopsy samples suggest emergence of SCLC genetic alterations before biopsy-proven SCLC, as shown by increasing variant allele frequency of TP53, RB1, PIK3CA alterations. ScRNA-seq revealed potential therapeutic targets including DLL3, CD276 (B7-H3) and PTK7 were widely expressed in transformed SCLC. ConclusionsSCLC transformation is a potential treatment resistance mechanism in driver-mutant NSCLC. In our cohort of 34 EGFR-mutant NSCLC, poor prognosis was observed after SCLC transformation. Clinicogenomic analyses of paired and longitudinal samples identified genomic alterations emerging post-transformation and scRNA-seq reveal potential therapeutic targets in this population. Further studies are needed to rigorously validate biomarkers and therapeutic targets for this patient population.

Rationale and Design of a Phase II Trial of Combined Serplulimab and Chemotherapy in Patients with Histologically Transformed Small Cell Lung Cancer: a Prospective, Single-arm and Multicentre Study

AimsTransformed small cell lung cancer (T-SCLC) is a highly aggressive clinical disease with a notably poor prognosis. It most often arises from epidermal growth factor receptor (EGFR)-mutant non-small cell lung cancer (NSCLC) following treatment. To date, no standard treatment has been established for T-SCLC. Platinum-etoposide was the most commonly used regimen, but progression-free survival remains unsatisfactory. Therefore, there is an urgent unmet need to develop novel and effective strategies for this population. Our study, a multicentre, open-label, single-arm phase II clinical trial (NCT05957510), aims to evaluate the efficacy and safety of serplulimab plus chemotherapy in untreated T-SCLC patients after histological transformation. Materials and methodsIn total, 36 eligible participants experiencing SCLC transformation from EGFR-mutant NSCLC will be enrolled to receive combination therapy of serplulimab, etoposide and carboplatin for four to six cycles, followed by maintenance therapy with serplulimab for up to 2 years. The primary endpoint is progression-free survival; secondary endpoints include objective response rate, overall survival and safety. ResultsEnrolment started in July 2023 and is ongoing, with an estimated completion date of December 2025. ConclusionsThis study aims to provide valuable insights into the efficacy and safety of combining serplulimab with chemotherapy for treating patients with T-SCLC originating from EGFR-mutant NSCLC.

Resistance to osimertinib in advanced EGFR-mutated NSCLC: a prospective study of molecular genotyping on tissue and liquid biopsies.

Resistance to osimertinib in advanced EGFR-mutated non-small cell lung cancer (NSCLC) constitutes a significant challenge for clinicians either in terms of molecular diagnosis and subsequent therapeutic implications. This is a prospective single-centre study with the primary objective of characterising resistance mechanisms to osimertinib in advanced EGFR-mutated NSCLC patients treated both in first- and in second-line. Next-Generation Sequencing analysis was conducted on paired tissue biopsies and plasma samples. A concordance analysis between tissue and plasma was performed. Sixty-five advanced EGFR-mutated NSCLC patients treated with osimertinib in first- (n = 56) or in second-line (n = 9) were included. We managed to perform tissue and liquid biopsies in 65.5% and 89.7% of patients who experienced osimertinib progression, respectively. Acquired resistance mechanisms were identified in 80% of 25 patients with post-progression samples, with MET amplification (n = 8), EGFR C797S (n = 3), and SCLC transformation (n = 2) the most frequently identified. The mean concordance rates between tissue and plasma for the EGFR activating mutation and for the molecular resistance mechanisms were 87.5% and 22.7%, respectively. Resistance to osimertinib demonstrated to be highly heterogeneous, with MET amplification the main mechanism. Plasma genotyping is a relevant complementary tool which might integrate tissue analysis for the study of resistance mechanisms.

Abstract 1167: Single-cell transcriptomic profiling of SCLC transformation reveals increased intratumoral diversity of variant and non-neuroendocrine subtypes

Abstract Lineage plasticity is the ability for a cell to change its phenotypic state under evolutionary pressure. This process mediates acquired resistance to EGFR-targeted therapies in lung adenocarcinoma (LUAD), through transformation to small cell lung cancer (SCLC), an aggressive cancer type of neuroendocrine (NE) histology. This transformed SCLC has worse clinical outcomes than either its LUAD or de novo SCLC counterparts, with less than one-year overall survival following transformation. Classical SCLC itself can display plasticity through interconversion between classical, variant, and non-NE transcriptional subtypes, with non-classical subtypes displaying increased metastasis and chemoresistance. It is poorly understood what factors drive SCLC transformation or subtype switching. Prior studies poorly model intratumoral heterogeneity because they profile tumors in bulk, which only estimates the average phenotype. However, SCLC transformation often results in admixed LUAD/SCLC tumors. We sought to capture the full intratumoral heterogeneity of SCLC transformation and identify potential molecular determinants of plasticity by applying single-cell RNA sequencing (scRNA-seq) to 41 tumors and patient-derived xenografts from 22 patients with transformed or combined LUAD/NE histology, with matched targeted DNA sequencing and 17 de novo SCLC tumors, 10 LUAD tumors with concurrent EGFR/RB1/TP53 mutations, and 4 tumor-adjacent normal lung samples for comparison. Of 234,322 single transcriptomes assessed, we found 89,113 NE cancer cells and 18,197 LUAD cancer cells. We confirmed that NE and LUAD components within the same tumor shared clonal mutations and common ancestry. Compared to de novo, transformed SCLC harbored greater phenotypic diversity across patients (p < 1 × 10−10), driven largely by enrichment of variant and non-NE subtypes (p < 0.02), including NEUROD1, POU2F3, and YAP1-high subtypes, the latter of which was completely absent in de novo. Within each tumor, transformed SCLC displayed higher intratumoral subtype diversity than de novo SCLC (likelihood ratio p < 0.025). After adjusting for SCLC subtype, differential expression and pathway analysis demonstrated that transformed SCLC is a distinct phenotype from de novo and shares features of the ancestral clone that include residual EGFR and NSCLC gene signatures, as well as pathways in neuronal stemness, MYC targets, AKT/MTOR signaling, JAK/STAT inflammation, and chromatin remodeling. In sum, we find increased intratumoral phenotypic diversity in transformed SCLC, including variant and non-NE subtypes, that may explain worse clinical outcomes. We show that transformed SCLC is a distinct phenotype from de novo, marked by pathways that may offer new potential drug targets to constrain plasticity, with the goal of restoring original sensitivity to targeted therapies. Citation Format: Joseph Minhow Chan, Alvaro Quintanal-Villalonga, Amin Sabet, Parvathy Manoj, Ojasvi Chaudhary, Tianhao Xu, Ignas Masilionis, Jacklynn Egger, Noor Sohail, Jaeyoung Chun, Tal Nawy, Linas Mazutis, Triparna Sen, Ronan Chaligne, Helena Yu, Dana Pe'er, Charles Rudin. Single-cell transcriptomic profiling of SCLC transformation reveals increased intratumoral diversity of variant and non-neuroendocrine subtypes [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 1167.

32P Atezolizumab plus albumin paclitaxel-based regimens is an optional treatment for EGFR-mutant patients with SCLC transformation after EGFR-TKI

32P Atezolizumab plus albumin paclitaxel-based regimens is an optional treatment for EGFR-mutant patients with SCLC transformation after EGFR-TKI

The comparison of chemotherapy and treatments according to NGS results in advanced lung adenocarcinoma patients resistant to EGFR-TKIs.

e21082 Background: There were no relative researches referring to optimal treatment strategy after the resistance to the first/second-generation EGFR-TKIs without T790M mutation or the third generation EGFR-TKIs as the first or second line therapy. Methods: Retrospective analysis was performed on the clinical and sequencing data obtained from 129 patients with advanced EGFR-mutant lung adenocarcinoma and disease progression on the prior EGFR-TKIs.The patients were divided into Chemotherapy group or Personalized group according the the therapies after acquired resistance to EGFR-TKIs. Results: 36 patients were enrolled in Personalized group and 93 in Chemotherapy group. Personalized group：22 patients with MET amplification received the combination therapy of EGFR-TKIs and MET inhibitors; 6 patients with SCLC transformation received EP/EC chemotherapy; 2 patients with BRAF mutation were treated with the combination of EGFR-TKIs, dabrafenib and trametinib; 3 patients with ERBB2 amplification were added Trastuzumab in the therapy; 2 patients with RET fusion were accepted LOXO-292 therapy; 1 patient had the combination therapy of the 1st and 3rd EGFR-TKIs because of T790m and C797S mutations in trans allelic context.Chemotherapy group: 79 patients received pemetrexed plus platinum therapy, 14 patients received paclitaxel plus platinum therapy. 12 patients achieved PR and 11 patients achieved SD in Personalized group, 48 PR, 25 SD in Chemotherapy group. The median PFS was 5.5 months in Chemotherapy group and 3.5 months in Personalized group, No significant differences were observed in ORR(p = 0.13), DCR(p = 0.12) and PFS(P = 0.26) between two group. Conclusions: Chemotherapy maybe is the optimal choice to patients with advanced EGFR-mutant lung adenocarcinoma and disease progression on the prior EGFR-TKI in current medical conditions.

Small Cell Lung Cancer Transformation following Treatment in EGFR-Mutated Non-Small Cell Lung Cancer.

EGFR-mutated lung adenocarcinoma patients who received tyrosine kinase inhibitors (TKIs) may initially respond to therapy, but over time, resistance eventually occurs. In a small population (5–10%), these patients can have a histological transformation to SCLC. Nine patients with EGFR-mutated lung adenocarcinoma who transformed to SCLC were evaluated at City of Hope. Patient clinical and pathology data, including multiple next-generation sequencing (NGS) results, clinical therapies, histology, and outcomes, were collected across multiple time points. Descriptive statistics were utilized to visualize and interpret the clinical therapeutic timeline and molecular transformation profiles for these patients. All patients received at least one line of EGFR TKI therapies prior to small cell lung cancer transformation, including erlotinib, afatinib, and osimertinib. Two patients also received chemotherapy prior to transformation (one with immunotherapy). The median months to small cell lung cancer transformation was 16 months, ranging from 4–49 months. The median overall survival (OS) was 29 months from diagnosis, with the minimum of 16 months and maximum of 62 months. The majority of patients had EGFR exon 19 deletion (n = 7, 77.8%), and no patients had a change of original oncogenic EGFR mutation over the different time points. Though a TP53 mutation was detected in eight patients (88.9%) either at the first biopsy or the subsequent biopsies, an RB1 alteration was only detected in one patient at presentation, and three patients upon subsequent biopsies (n = 4, 44.4%). Each patient had a unique molecular profile in the subsequent molecular testing post-transformation, but BRAF alterations occurred frequently, including BRAF rearrangement (n = 1), fusion (n = 1), and amplification (n = 1). Our results showed that EGFR-mutated lung adenocarcinoma to SCLC transformation patients have a unique histological, molecular, and clinical profile over multiple time points, with further heterogeneity that is not currently reported in the literature, and we suggest more work is required to better understand the molecular heterogeneity and clinical outcomes over time for this EGFR TKI resistance subtype.

Evolution and genotypic characteristics of small cell lung cancer transformation in non-small cell lung carcinomas

BackgroundSmall cell lung cancer (SCLC) transformation had previously been reported mainly in epidermal growth factor receptor (EGFR) mutant adenocarcinoma. However, the underlying genomic profile remains unclear. Our study aimed to find the evolution and genotypic characteristic of SCLC transformation. MethodsThirty-one SCLC transformation patients who were initially diagnosed as non-small cell lung cancer (NSCLC) patients were included. Whole exome sequencing (WES) of both primary and transformed re-biopsy lesions was conducted on 12 patients. Clinical characteristics were analyzed using R software (v.3.6.1). ResultsOur study included 31 patients, of whom, three had lung squamous cell carcinoma, 6 patients did not carry EGFR mutations, and 30 patients received chemotherapy for SCLCs. The disease control rate (DCR) was 96.7%, and the median progression-free survival (PFS) was 4.03 months. The median time to transformation was 33.07 months, and the median overall survival (OS) was 62.08 months. Somatic mutation analysis showed that besides TP53, RB1, and EGFR, there was a high occurrence of mutations to CSMD3 and ADAMTS19, especially in the EGFR-wild type (EGFR-wt) group. Concerning mutational signature, the EGFR-mutant (EGFR-mut) transformed group favored an apolipoprotein B (APOBEC) mRNA editing catalytic polypeptide-like-associated mutation pattern (P = 0.16). DNA damage repair (DDR)-related signatures were significantly enriched in the EGFR-wt transformed group (P = 0.034). Additionally, clonal evolution analysis revealed that all patients had the same main trunk genes in the phylogenetic tree. Transformed SCLCs are not sensitive to immunotherapy, possibly due to increased tumor heterogeneity. ConclusionsOur results indicate that the EGFR-wt patients could also transform to SCLCs, but they have different genetic features with EGFR-mut patients. SCLC-transformed patients respond to classical chemotherapy and have a better prognosis than those with classical SCLCs.

Mechanisms and management of 3rd‑generation EGFR‑TKI resistance in advanced non‑small cell lung cancer (Review)

Targeted therapy with epidermal growth factor receptor (EGFR)-tyrosine kinase inhibitors (TKIs) is a standard modality of the 1st-line treatments for patients with advanced EGFR-mutated non-small cell lung cancer (NSCLC), and substantially improves their prognosis. However, EGFR T790M mutation is the primary mechanism of 1st- and 2nd-generation EGFR-TKI resistance. Osimertinib is a representative of the 3rd-generation EGFR-TKIs that target T790M mutation, and has satisfactory efficacy in the treatment of T790M-positive NSCLC with disease progression following use of 1st- or 2nd-generation EGFR-TKIs. Other 3rd-generation EGFR-TKIs, such as abivertinib, rociletinib, nazartinib, olmutinib and alflutinib, are also at various stages of development. However, the occurrence of acquired resistance is inevitable, and the mechanisms of 3rd-generation EGFR-TKI resistance are complex and incompletely understood. Genomic studies in tissue and liquid biopsies of resistant patients reveal multiple candidate pathways. The present review summarizes the recent findings in mechanisms of resistance to 3rd-generation EGFR-TKIs in advanced NSCLC, and provides possible strategies to overcome this resistance. The mechanisms of acquired resistance mainly include an altered EGFR signaling pathway (EGFR tertiary mutations and amplification), activation of aberrant bypassing pathways (hepatocyte growth factor receptor amplification, human epidermal growth factor receptor 2 amplification and aberrant insulin-like growth factor 1 receptor activation), downstream pathway activation (RAS/RAF/MEK/ERK and PI3K/AKT/mTOR) and histological/phenotypic transformations (SCLC transformation and epithelial-mesenchymal transition). The combination of targeted therapies is a promising strategy to treat osimertinib-resistant patients, and multiple clinical studies on novel combined therapies are ongoing.

Histological transformation of non-small cell lung cancer: Clinical analysis of nine cases.

BACKGROUNDHistological transformation is one of the numerous mechanisms of acquired resistance to epidermal growth factor receptor tyrosine kinase inhibitors (EGFR-TKIs). Given its rarity, the underlying transformational mechanisms, clinical features, and therapeutic prognoses are only studied through limited case reports.AIMTo analyze the clinical characteristics and underlying mechanisms in non-small cell lung cancer (SCLC) patients with histological transformation after treatment with EGFR-TKIs.METHODSWe retrospectively investigated nine patients diagnosed with non-SCLC transforming to SCLC, large-cell neuroendocrine carcinoma (LCNEC), or squamous cell carcinoma on re-biopsy after first- or third-generation EGFR-TKIs.RESULTSThe median age of nine patients was 60 years. Among them, six patients had the EGFR 19del mutation, one had the L858R mutation, and one had wild-type EGFR. The level of plasma NSE was measured in six patients with SCLC or LCNEC transformation when transformation occurred, and five patients had elevated plasma NSE levels. All patients received standard chemotherapy after transformation with the exception of one patient who received chemotherapy and anlotinib.CONCLUSIONTumor re-biopsy should be performed routinely when EGFR-TKI therapy fails in lung cancer patients to avoid ignoring histological transformation and to select a subsequent therapeutic strategy. The transformed tumor retained the original EGFR mutation, indicating that histological transformation represents an evolution from the initial tumor.

Abstract 5882: Genomic correlates of differential response to EGFR-directed tyrosine kinase inhibitors

Abstract Background: Oncogenic mutations in EGFR are powerful biomarkers of response to EGFR tyrosine kinase inhibitors (TKIs) in non-small cell lung cancer (NSCLC). However, there remains significant heterogeneity in duration of response to therapy and overall survival. TP53 mutations have been linked with worse outcomes, thought to be due to increased likelihood of small cell transformation. Methods: We identified NSCLC patients at our institution with sensitizing oncogenic EGFR mutations who had been treated with EGFR TKI(s) and who had at least one tumor specimen profiled via targeted next generation sequencing (OncoPanel). Progression free survival (PFS) on first-line EGFR TKI, overall survival (OS), and resistance mechanism were assessed. Patients were defined as TP53 mutant positive (TP53+) or wild type (TP53-). Pathogenic TP53 mutations were identified and associated with outcome and resistance mechanism. Results: We identified 270 patients for inclusion in our cohort. 70% were female (190/270), 60% were never smokers (163/270), and median age was 62 (range 29-93). Sensitizing EGFR mutations were predominantly exon 19 deletion (51%, 138/270) or L858R (38%, 103/270). 94% of patients were treated with first-line erlotinib (253/270), and 30% received second-line osimertinib (82/270). TP53+ patients were as likely to achieve objective radiographic response as TP53- (p=0.615), but had shorter PFS (HR 1.56, CI 1.1-2.2, p=0.011). TP53+ patients were no more likely to develop SCLC transformation (p=0.637). Among patients with T790M as their resistance mechanism, TP53+ patients still had shorter PFS compared to TP53- (HR 1.9, CI 1.2-3, p=0.003). Pre-treatment TP53 mutations were associated with a higher tumor mutational burden (p=0.017) and copy number burden (p=0.0026). Conclusion: While TP53 mutations associate with shorter PFS, there is no association with baseline TP53 mutation status and small cell transformation, and TP53+ patients also develop the T790M resistance mutation earlier than TP53- patients. Higher mutation and copy number burden in TP53+ patients suggests greater genomic instability and may act as a mechanism of earlier resistance development. Citation Format: Natalie Vokes, Tom Nguyen, Christine Lydon, Emily Chambers, Lynette Sholl, Mizuki Nishino, Eliezer Van Allen, Pasi Janne. Genomic correlates of differential response to EGFR-directed tyrosine kinase inhibitors [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 5882.

Patients with advanced non-small cell lung cancer with EGFR mutations in addition to complex mutations treated with osimertinib have a poor clinical outcome: A real-world data analysis.

The present study aimed to investigate the clinical characteristics and outcomes of patients with advanced non-small cell lung cancer (NSCLC) treated with osimertinib, and focused on the resistance mechanism to osimertinib in a real-world setting. Data from 128 patients with advanced NSCLC who were treated with osimertinib between March 2015 and November 2018 at the Chinese People's Liberation Army General Hospital (Beijing, China) were retrospectively collected, and the associations between mutation types and survival were analysed. In patients treated with osimertinib, the objective response rate reached 60.9% (78/128) and the disease control rate reached 81.3% (104/128), with a median progression-free survival (PFS) time of 12.2 months. A number of complex mutations were identified in the re-analysis after the development of osimertinib resistance, including TP53, KRAS and PIK3CA mutations, epidermal growth factor receptor (EGFR) and MYC amplifications, and mutations associated with SCLC transformation, demonstrating that these mutations may account for osimertinib resistance. The median PFS time for patients with the EGFR T790M mutation (n=41) was significantly longer than that for patients with the T790M mutation and the aforementioned complex mutations (n=13) (16.7 vs. 10.8 months; P=0.001). Patients with a single EGFR mutation (n=87) had a longer median PFS time than those with an EGFR mutation and complex mutations (n=24) (14.63 vs. 6.63 months; P<0.0001). In conclusion, the present study analysed the effects of osimertinib in patients with advanced NSCLC with EGFR mutations, particularly T790M mutations. The results indicated that the efficacy of osimertinib was weakened when patients had complex mutations, suggesting that complex mutations may be responsible for resistance to osimertinib.

Emerging Treatment Paradigms for EGFR-Mutant Lung Cancers Progressing on Osimertinib: A Review.

Since its approval in April 2018, osimertinib has been widely adopted as first-line therapy for patients with advanced EGFR-mutant non -small cell lung cancer (NSCLC). Understanding osimertinib resistance mechanisms and currently available treatment options are essential to selecting optimal second line therapy for patients whose disease progresses during front-line osimertinib. Using data compiled from 6 osimertinib-resistance series, we describe here the heterogeneous profile of EGFR-dependent and independent mechanisms of osimertinib treatment failure. We identified MET alterations (7%-24%), EGFR C797X (0%-29%), SCLC transformation (2%-15%), and oncogene fusions (1%-10%) as the most common mechanisms of resistance. This review provides an evidence-based, algorithmic approach to the evaluation and management of post-osimertinib progression as well as a compendium of active, enrolling clinical trials for this population.

High Prevalence of Somatic Oncogenic Driver Alterations in Patients With NSCLC and Li-Fraumeni Syndrome.

Actionable somatic molecular alterations are found in 15% to 20% of NSCLC in Europe. NSCLC is a tumor observed in patients with germline TP53 variants causing Li-Fraumeni syndrome (LFS), but its somatic molecular profile is unknown. Retrospective study of clinical and molecular profiles of patients with NSCLC and germline TP53 variants. Among 22 patients with NSCLC and LFS (n= 23 lung tumors), 64% were women, median age was 51 years, 84% were nonsmokers, 73% had adenocarcinoma histological subtype, and 84% were diagnosed with advanced-stage disease. These patients harbored 16 distinct germline TP53 variants; the most common was p.R158H (5/22; three in the same family). Personal and family histories of cancer were reported in 71% and 90% of patients, respectively. In most cases (87%, 13/15), lung cancer was diagnosed with a late onset. Of the21 tumors analyzed, somatic oncogenic driver mutations were found in 19 of 21 (90%), EGFR mutations in 18 (exon 19 deletion in 12 cases, L858R in three cases, and G719A, exon 20 insertion, and missing mutation subtype, each with one case), and ROS1 fusion in one case. A PI3KCA mutation was concurrently detected at diagnosis in three EGFR exon 19-deleted tumors (3/12). The median overall survival was 37.3 months in 14 patients treated with EGFR inhibitors; seven developed resistance, five (71%) acquired EGFR-T790M mutation, and one had SCLC transformation. Driver oncogenic alterations were observed in 90% of the LFS tumors, mainly EGFR mutations; one ROS1 fusion was also observed. The germline TP53 variants and lung cancer carcinogenesis driven by oncogenic processes need further evaluation.

Transformation to small cell lung cancer as a mechanism of resistance to immunotherapy in non-small cell lung cancer

ObjectivesNon-small cell lung cancer (NSCLC) is the leading cause of cancer-related death world-wide. Immune checkpoint inhibitors (ICI) have become the most promising type of treatment in oncology in general, and significantly so in NSCLC. Limited data is available about mechanisms of primary resistance. Data is lacking about mechanisms involved in acquired resistance or mixed responses in NSCLC. We aimed to identify mechanisms of resistance by studying biopsies taken from sites of secondary progression. Materials and methodsWe identified all cases of NSCLC that have received ICI for advanced disease in our institute. Of these cases, those that have demonstrated acquired resistance or mixed responses, and have underwent a biopsy from a progressive lesion were analyzed. Selected specimens were subjected to next-generation sequencing (NGS; Oncomine™ Solid Tumour Fusion Transcript Kit). ResultsOut of 664 lung cancer cases, 249 were NSCLC that have received ICI. Of these, eight cases matched our search criteria. Two of them demonstrated transformation to small cell lung cancer (SCLC; 2/8, 25%). NGS verified a common origin to a matched pre-treatment NSCLC specimen and an on-treatment progressive SCLC specimen. In two cases no tumor cells were found and in the remaining four the pathology was similar to the initial biopsy. In one of the cases of SCLC transformation platinum-etoposide chemotherapy was administered, with short-term benefit only and further disease progression. ConclusionMechanisms of acquired resistance to ICI include SCLC transformation. Repeat biopsies of progressing lesions after initial response or in cases of mixed response can shed light on mechanisms of resistance.

EP1.12-09 EGFR-Mutant Adenocarcinoma Transform into Small-Cell Lung Cancer: Real or Not

Small-cell transformation is well known as one of the acquired resistance mechanism to EGFR-tyrosine kinase inhibitors (TKIs), nevertheless we recently found an interesting phenomenon that most small-cell transformations actually are combined small-cell lung cancer before TKI treatments rather than pure adenocarcinoma. We retrieved 13 patients with former pathological diagnosis of adenocarcinoma before TKI therapies from 1,082 cases with SCLC component and compared the previous biopsy results of the these cases. All the previous adenocarcinomas slides were gathered and were reviewed one by one carefully again by an advanced pathologist. All patients were stage IV EGFR-mutant adenocarcinomas and treated with EGFR-TKIs before SCLC transformation diagnosed. After their disease progress, re-biopsy were performed to identify resistance mechanism. Previous pathology showed only one patient was diagnosed with combined SCLC mixed with adenocarcinoma before TKI, the rest 12 cases were pathologically diagnosed of pure adenocarcinoma and identified as small-cell transformation. We amazingly found that 9 of 12 patients actually contained very few SCLC component when we reviewed these cases, varying from less than 1% to 5%. Dubious SCLC components were found in two patients. Only one patient was a real small-cell transformation and we didn’t find any SCLC mixture on previous adenocarcinoma sections. In conclude about 75% (9/12) of cases originally diagnosed with small-cell transformation were actually pseudo-small-cell transformation. Combined SCLC with very few SCLC components were prone to be misdiagnosed into pure adenocarcinoma. Most metastatic lung cancers were diagnosed with small biopsy, in which the potential mixture of SCLC was much more easily to miss, so the pseudo-small-cell transformation may be more common than estimate in real world. It’s worth noting that careful review again of the previous adenocarcinoma sections is essential before diagnosis of small-cell transformation.