RET Fusion Research Articles

Utility of the Ba/F3 cell system for exploring on-target mechanisms of resistance to targeted therapies for lung cancer.

Molecular targeted therapies are the standard of care for front‐line treatment of metastatic non‐small‐cell lung cancers (NSCLCs) harboring driver gene mutations. However, despite the initial dramatic responses, the emergence of acquired resistance is inevitable. Acquisition of secondary mutations in the target gene (on‐target resistance) is one of the major mechanisms of resistance. The mouse pro‐B cell line Ba/F3 is dependent on interleukin‐3 for survival and proliferation. Upon transduction of a driver gene, Ba/F3 cells become independent of interleukin‐3 but dependent on the transduced driver gene. Therefore, the Ba/F3 cell line has been a popular system to generate models with oncogene dependence and vulnerability to specific targeted therapies. These models have been used to estimate oncogenicity of driver mutations or efficacies of molecularly targeted drugs. In addition, Ba/F3 models, together with N‐ethyl‐N‐nitrosourea mutagenesis, have been used to derive acquired resistant cells to investigate on‐target resistance mechanisms. Here, we reviewed studies that used Ba/F3 models with EGFR mutations, ALK/ROS1/NTRK/RET fusions, MET exon 14 skipping mutations, or KRAS G12C mutations to investigate secondary/tertiary drug resistant mutations. We determined that 68% of resistance mutations reproducibly detected in clinical cases were also found in Ba/F3 models. In addition, sensitivity data generated with Ba/F3 models correlated well with clinical responses to each drug. Ba/F3 models are useful to comprehensively identify potential mutations that induce resistance to molecularly targeted drugs and to explore drugs to overcome the resistance.

Identification and Validation of Noncanonical RET Fusions in Non–Small-Cell Lung Cancer through DNA and RNA Sequencing

RET fusion has emerged as a targetable driver in non-small-cell lung cancer. A comparative analysis on RET fusions at DNA [DNA sequencing (DNA-seq)] and RNA [RNA sequencing (RNA-seq)] levels was performed in this study. Archived tumor samples from 54 non-small-cell lung cancer patients with DNA-level noncanonicalRETfusions were selected for RNA-seq. RNA-seq identified RET fusion transcripts in 41 of 44 samples passing quality control. In the subset of cases harboring RET 3'-end fusions and predicted to produce in-frame proteins (group A; n=33), RNA-seq identified the same 3'-end fusions in 32 (96.9%). A total of 26 of 32 also had a reciprocal RET 5'-end fusion detected by DNA-seq that was not transcribed. In the subset with DNA-level out-of-frame RET fusions (group B; n=9), RNA-seq identified in-frame RET fusion transcripts in 8 cases (88.9%). In the subset only identified with a RET 5'-end fusion by DNA-seq (group C; n=2), RNA-seq detected the corresponding 3'-end fusion in one case. The discordant DNA- and RNA-level fusions observed in group B may be mediated by complex genomic rearrangement events and transcriptional or post-transcriptional processes. In conclusion, DNA-seq demonstrates a high concordance of 96.9% on detecting in-frame RET fusion, but shows a low concordance on detecting out-of-frame RET fusion and RET 5'-end fusion compared with RNA-seq.

Molecular Testing and Treatment Strategies in RET-Rearranged NSCLC Patients: Stay on Target to Look Forward

RET alterations are recognized as key oncogenic drivers in different cancer types, including non-small cell lung cancer (NSCLC). Multikinase inhibitors (MKIs) with anti-RET activities resulted in variable efficacy with significant toxicities because of low target specificity. Selective RET kinase inhibitors, such as pralsetinib and selepercatinib, demonstrated high efficacy and favorable tolerability in advanced RET-rearranged NSCLC patients, leading to their introduction in the clinical setting. Among the different approaches available for the identification of RET rearrangements, next-generation sequencing (NGS) assays present substantial advantages in terms of turnaround time and diagnostic accuracy, even if potentially limited by accessibility issues. The recent advent of novel effective targeted therapies raises several questions regarding the emergence of resistance mechanisms and the potential ways to prevent/overcome them. In this review, we discuss molecular testing and treatment strategies to manage RET fusion positive NSCLC patients with a focus on resistance mechanisms and future perspectives in this rapidly evolving scenario.

Fusion Oncogenes Are Associated With Increased Metastatic Capacity and Persistent Disease in Pediatric Thyroid Cancers.

In 2014, data from a comprehensive multiplatform analysis of 496 adult papillary thyroid cancer samples reported by The Cancer Genome Atlas project suggested that reclassification of thyroid cancer into molecular subtypes, RAS-like and BRAF-like, better reflects clinical behavior than sole reliance on pathologic classification. The aim of this study was to categorize the common oncogenic variants in pediatric differentiated thyroid cancer (DTC) and investigate whether mutation subtype classification correlated with the risk of metastasis and response to initial therapy in pediatric DTC. Somatic cancer gene panel analysis was completed on DTC from 131 pediatric patients. DTC were categorized into RAS-mutant (H-K-NRAS), BRAF-mutant (BRAF p.V600E), and RET/NTRK fusion (RET, NTRK1, and NTRK3 fusions) to determine differences between subtype classification in regard to pathologic data (American Joint Committee on Cancer TNM) as well as response to therapy 1 year after initial treatment had been completed. Mutation-based subtype categories were significant in most variables, including age at diagnosis, metastatic behavior, and the likelihood of remission at 1 year. Patients with RET/NTRK fusions were significantly more likely to have advanced lymph node and distant metastasis and less likely to achieve remission at 1 year than patients within RAS- or BRAF-mut subgroups. Our data support that genetic subtyping of pediatric DTC more accurately reflects clinical behavior than sole reliance on pathologic classification with patients with RET/NTRK fusions having worse outcomes than those with BRAF-mutant disease. Future trials should consider inclusion of molecular subtype into risk stratification.

Frankly Invasive Carcinoma Ex-intraductal Carcinoma: Expanding on an Emerging and Perplexing Concept in Salivary Gland Tumor Pathology.

Intraductal carcinoma (IDC) of the salivary glands is an uncommon and enigmatic tumor, our understanding of which is rapidly evolving. Recent studies have demonstrated multiple IDC subtypes and consistent gene fusions, most frequently involving RET. Because IDC is a ductal proliferation surrounded by flattened myoepithelial cells, it was previously presumed to be analogous to breast ductal carcinoma in situ, but recent evidence has shown that the myoepithelial cells of fusion-positive IDC harbor the same genetic alterations of the ductal cells and are therefore neoplastic. In addition, there are rare reports of fusion-positive IDC with overt areas of irregular invasion lacking myoepithelial cells, but this phenomenon is not well documented or understood. This study aims to better characterize these frankly invasive carcinoma ex-IDC. All cases of frankly invasive carcinoma ex-IDC were obtained from the authors' files. Inclusion criteria included a component of concurrent or antecedent IDC and/or a fusion known to be associated with IDC. Immunohistochemistry (S100, SOX10, mammaglobin, androgen receptor, p63, p40) and molecular analysis (targeted RNA sequencing or large panel DNA next generation sequencing) was performed. Clinical follow-up was obtained from medical records. Ten cases of frankly invasive carcinoma ex-IDC were identified. The tumors occurred in 8 men and 2 women ranging from 33 to 82 years (mean, 66.3). All but one case arose in the parotid gland. In 4 cases, the IDC component was intercalated duct type. It was mixed apocrine/intercalated duct in two, and in the remaining 4 cases, no residual IDC was identified. The frankly invasive carcinomas were remarkably heterogeneous, ranging from minimally to widely invasive beyond the confines of the IDC, low-grade to high-grade, with morphologies that varied from duct-forming to those having clear cell or sarcomatoid features, to frankly apocrine. The original diagnoses for these cases were (adeno) carcinoma, not otherwise specified (n = 6), salivary duct carcinoma (n = 3), and secretory carcinoma (n = 1). All cases harbored fusions: NCOA4::RET (n = 6), TRIM33::RET (n = 2), TRIM27::RET (n = 1), and STRN::ALK (n = 1). Clinically, one tumor recurred locally, cervical lymph node metastases occurred in five patients, and distant metastasis later developed in four of these patients. Our findings highlight striking diversity in frankly invasive carcinomas that arise from fusion-positive IDC, a tumor which may serve as a precursor neoplasm like pleomorphic adenoma. These carcinomas vary in their extent of invasion, grade, histologic appearances, and clinical behavior. Importantly, in contrast to pure IDC, which is believed to be indolent, many frankly invasive cases were aggressive. Because RET and ALK fusions are targetable, it is important to recognize the broad spectrum of frankly invasive carcinomas that can arise from IDC, particularly because some cases are completely overrun or recur without any recognizable IDC component. These results suggest fusion analysis may be of clinical benefit on any salivary gland (adeno) carcinoma, not otherwise specified or salivary duct carcinoma.

Next-generation Sequencing Reveals Age-dependent Genetic Underpinnings in Lung adenocarcinoma.

Background: More than 40% of lung cancer patients are diagnosed at ages over 70. However, the genomic and clinical characteristics among them remain elusive. Here, we performed targeted capture sequence to characterize the mutational spectrum of Chinese lung adenocarcinoma (LUAD) patients across ages.Patients and Methods: 2025 LUAD patients were divided into three groups: young (≤50 years old) (n=416, 20.54%), intermediate (51~69 years old) (n=1271, 62.77%), and aged (≥70 years old) (n=338, 16.69%). 1,021-gene panel and 59-gene panel were used for sequencing with tissue samples. Genetic alterations and tumor mutation burden (TMB) in LUAD patients were investigated.Results: The frequency of mutations affecting 20 genes were significantly higher in aged group than in young group, and fourteen of them were not reported before, including involved in cell cycle/apoptosis signaling (FAT1, FAT2), DNA damage repair (FANCA and FANCM), chromatin histone modification (KDM6A), RTK/RAS/PI3K signaling (FLT4 and MTOR), NOTCH signaling (NOTCH1, NOTCH2 and NOTCH4) and other signaling pathway or cellular regulatory factor (KEAP1, ASXL1, EPHB1 and ABCB1). Six previously reported mutated genes (RBM10, KRAS, LRP1B, CDKN2A and KMT2C/D) were also significantly more frequent in aged group. Among clinical actionable mutation sites, KRAS mutation was presented more common in aged group; both MET exon 14 skipping and MET amplification were significantly positively correlated with old age; the fusions of ALK, ROS1, RET and ERBB2 exon 20 insertion were less frequent in aged group. Furthermore, a higher level of TMB was found in aged group compared with young group.Conclusion: In this study, we revealed the differences of somatic genetic mutations and TMB between young and aged LUAD patients, which may provide directions of targeted therapy and advantages of immunotherapy for the elderly in the future.

Genomic Profiling of Aggressive Thyroid Cancer in Association With its Clinicopathological Characteristics.

Poorly differentiated thyroid carcinoma (PDTC), anaplastic thyroid carcinoma (ATC), and advanced DTC have poor outcomes. We performed next-generation sequencing in nine selected aggressive thyroid cancers. Among the nine patients, the driver gene mutations BRAF V600E (3/9) and NRAS Q61K (1/9) were detected. Other oncogenic mutations included ERBB2 (1/9) and CDK4 (1/9). Telomerase reverse transcriptase (TERT) promoter mutation was found in five cases. Among tumor suppressor genes, mutations in TP53 (3/9), ARID1A (1/9), APC (1/9), MEN1 (1/9), DICER1 (1/9), and MED12 (1/9) were identified. RET fusions were found in two cases, one with PTDC and the other with ATC. The ATC with RET fusion also harbored TP53 and TERT promoter mutations. None of the PDTC cases had BRAF or RAS gene alterations. Since genetic alterations with therapeutic and prognostic implications were detected using next-generation sequencing, this technique is recommended to be performed for patients with aggressive thyroid cancer.

Olfactomedin 4 Is Not a Precise Marker for Human Intestinal Stem Cells, But Is Involved in Intestinal Carcinogenesis

Olfactomedin 4 Is Not a Precise Marker for Human Intestinal Stem Cells, But Is Involved in Intestinal Carcinogenesis

Systematic population-based identification of NTRK and RET fusion-positive thyroid cancers.

ObjectiveThe aim of the study was to identify patients with NTRK fusion-positive or RET fusion/mutation-positive thyroid cancers, who could benefit from neurotrophic tyrosine kinase receptor (NTRK) or receptor tyrosine kinase (RET) inhibitors.MethodsPatients were identified in the Calgary prospective thyroid cancer database (N= 482). Patients were ‘pre-screened’ with clinically available MassARRAY® BRAF test, Colon Panel, Melanoma Panel, or ThyroSPEC™. Mutation-negative tumors were ‘screened’ for NTRK fusions and RET fusions/mutations with the Oncomine™ Comprehensive Assay v3 (OCAv3).ResultsA total of 86 patients were included in 1 of 2 separate analyses. Analysis A included 42 patients with radioactive iodine (RAI)-resistant distant metastases. After pre-screening, 20 BRAF and RAS mutation-negative patients underwent OCAv3 screening, resulting in the detection of 4 patients with NTRKfusions and 4 patients with RET fusions (8/20, 40% of analyzed patients). Analysis B included 44 patients, 42 with American Thyroid Association (ATA) high and intermediate risk of recurrence and 2 with medullary thyroid carcinoma. During pre-screening, 1 patient with an NTRK fusion, 1 patient with a RET fusion, and 30 patients with BRAF mutations were identified. The remaining 9 patients received OCAv3 screening, resulting in detection of 1 patient with an NTRKfusion and 1 with a RET fusion (4/11, 36% of analyzed patients).ConclusionsOur findings indicate a higher rate of NTRK fusions and RETfusions in patients with thyroid cancer with RAI-resistant distant metastases and ATA high or intermediate risk of recurrence. This highlights the importance of early screening to enable intervention with a NTRK or RET inhibitor.

Abstract P233: TAS0953/HM06 is effective in preclinical models of diverse tumor types driven by RET alterations

Abstract Fusions involving RET receptor tyrosine kinase are a common driver of tumors across different tissue types, such as lung, thyroid, colorectal, soft tissue and others. TAS0953/HM06 (hereby referred to as HM06) is a novel 2ndgeneration RET-specific inhibitor that is effective against RET solvent front (G810) and gatekeeper (V804) mutations. Here, we evaluated the efficacy of HM06 in lung and thyroid carcinomas, and soft-tissue sarcoma cell lines and PDXs derived from RET inhibitor-naive tumor samples or from tumors with acquired resistance to selpercatinib. HM06 was more effective than the RET multi-kinase inhibitors cabozantinib and vandetanib, and as effective as selpercatinib and pralsetinib in inhibiting growth of patient-derived and isogenic lung, thyroid and sarcoma cell lines (IC50=0.02-0.1 µM) harboring different RET fusions (KIF5B-RET, CCDC6-RET, TRIM33-RET, SPECCL1-RET) or activating mutations (RET C634W). Growth of non-tumor cells was up to 80-fold less sensitive to HM06 (IC50= 1.6 µM). Treatment of RET fusion-positive lung cancer cells with HM06 resulted in a dose-dependent inhibition of RET phosphorylation (Y905 and Y1062) and the downstream effectors AKT, ERK1/2, p70S6K and S6. Caspase 3/7 activity and markers of apoptosis (BIM, cleaved PARP) were induced by HM06 to a similar extent as pralsetinib and selpercatinib (dose range: 0.05-1 µM). HM06 induced changes in the core mediators of cell cycle regulation (upregulation of p27, downregulation of CCND1) and suppressed expression of MYC and ETV5. In vivo, HM06 blocked tumor growth and/or induced regression of up to 65% in seven patient-derived xenograft (PDX) models with RET fusions (five NSCLC PDXs, one sarcoma PDX and one NSCLC cell-line xenograft) to a similar extent as pralsetinib and selpercatinib. However, 6 weeks after cessation of treatment of the SPECCL1-RET-driven sarcoma PDX model, growth of tumors treated with HM06 was suppressed completely, whereas 3/5 pralsetinib-treated tumors and 1/5 selpercatinib-treated tumor regrew. Combination of HM06 and the MET inhibitor capmatinib effectively blocked growth of PDX tumors in a model that was derived from a patient sample that expressed RET fusion and METamplification, and was resistant to selpercatinib. These results suggest that HM06 may be an effective therapy for RET-driven tumors in a tissue-type agnostic manner and can effectively address common on-target and off-target resistance mechanisms such as RET G810X and V804X mutations. HM06 is currently in a phase 1 and 2 clinical trial for patients with advanced solid tumors with RET gene abnormalities (margaRET, NCT 04683250). Citation Format: Igor Odintsov, Renate I. Kurth, Kota Ishizawa, Lukas Delasos, Allan J.W. Lui, Inna Khodos, Connor J. Hagen, Qing Chang, Marissa S. Mattar, Morana Vojnic, Siddharth Kunte, Annalisa Bonifacio, Claudio Giuliano, Elisa De Stanchina, Emily Cheng, Emanuela Lovati, Marc Ladanyi, Romel Somwar. TAS0953/HM06 is effective in preclinical models of diverse tumor types driven by RET alterations [abstract]. In: Proceedings of the AACR-NCI-EORTC Virtual International Conference on Molecular Targets and Cancer Therapeutics; 2021 Oct 7-10. Philadelphia (PA): AACR; Mol Cancer Ther 2021;20(12 Suppl):Abstract nr P233.

Immunotherapy in Non-Small Cell Lung Cancer With Actionable Mutations Other Than EGFR.

While first line targeted therapies are the current standard of care treatment for non-small cell lung cancer (NSCLC) with actionable mutations, the cancer cells inevitably acquire resistance to these agents over time. Immune check-point inhibitors (ICIs) have improved the outcomes of metastatic NSCLC, however, its efficacy in those with targetable drivers is largely unknown. In this manuscript, we reviewed the published data on ICI therapies in NSCLC with ALK, ROS1, BRAF, c-MET, RET, NTRK, KRAS, and HER2 (ERBB2) alterations. We found that the objective response rates (ORRs) associated with ICI treatments in lung cancers harboring the BRAF (0–54%), c-MET (12–49%), and KRAS (18.7-66.7%) alterations were comparable to non-mutant NSCLC, whereas the ORRs in RET fusion NSCLC (less than10% in all studies but one) and ALK fusion NSCLC (0%) were relatively low. The ORRs reported in small numbers of patients and studies of ROS1 fusion, NTRK fusion, and HER 2 mutant NSCLC were 0–17%, 50% and 7–23%, respectively, making the efficacy of ICIs in these groups of patients less clear. In most studies, no significant correlation between treatment outcome and PD-L1 expression or tumor mutation burden (TMB) was identified, and how to select patients with NSCLC harboring actionable mutations who will likely benefit from ICI treatment remains unknown.

Abstract P06-02: Discovery of TAS0953/HM06, a novel next generation RET-specific inhibitor capable of inhibiting RET solvent front mutations

Abstract RET gene fusions are oncogenic drivers in multiple tumor types and are estimated to be present in 1% to 2% of non-squamous non-small cell lung cancers (NSCLCs). Although the first-generation selective RET inhibitors selpercatinib and pralsetinib show clinical antitumor activity in NSCLCs, acquired resistances driven by RET solvent front mutation (G810R/S/C) have emerged. In such cases, no other treatment options are currently available for these patients after relapse with selpercatinib or pralsetinib. TAS0953/HM06, a novel adenosine triphosphate-competitive and highly selective RET inhibitor, is a next-generation RET inhibitor that may overcome solvent front mutant resistance. We performed a panel test of 254 kinases and found that 23-nM TAS0953/HM06 displayed only RET inhibition as plotted over 50% inhibited kinases. TAS0953/HM06 potently inhibits recombinant wild-type (WT) RET at sub-nanomolar concentrations that are similar to the IC50 values of selpercatinib and pralsetinib in WT RET. We investigated the cellular potencies against RET WT fusions and RET mutations, including the gatekeeper mutations V804L/M and selpercatinib- or pralsetinib-resistant mutations G810R/S, in engineered BA/F3 cells. TAS0953/HM06 inhibited the growth of the RET fusion overexpressed in Ba/F3 cells, including both the V804M/L and G810R/S RET mutations and WT RET. In addition, we examined the crystal structure of the RET kinase domain complexed with an analogue of TAS0953/HM06. X-ray crystal structures of the complex revealed that the analogue has unique binding mode to RET respect to selpercatinib and pralsetinib: it does not fill the space in the direction of the side chain of G810, suggesting that TAS0953/HM06 effectively circumvents steric hindrance from solvent front substitutions. This feature likely contributes to the ability of TAS0953/HM06 to maintain its biological potency in G810 mutations. Finally, we evaluated the antitumor activity of various doses of TAS0953/HM06 in xenograft tumor model derived from Ba/F3 cells from mice expressing WT or G810R KIF5B-RET (these mice show resistance to selpercatinib and pralsetinib). A Doses as low as of 10 mg/kg twice a day, TAS0953/HM06 were able to significantly inhibit tumor growth and phospho-RET. Taken together, the results show that, in addition to its selective high potency against WT RET, TAS0953/HM06 shows significant potency against G810R solvent front mutation which is highly resistant to selpercatinib and pralsetinib, in vitro and in vivo. Therefore, TAS0953/HM06 might represent a new therapeutic option for patients with RET mutations, including those resistant to 1st generation selective RET inhibitors. The safety and efficacy of TAS0953/HM06 are currently being investigated in a phase 1/2 clinical trials (NCT04683250). Citation Format: Isao Miyazaki, Keiji Ishida, Masanori Kato, Tatsuya Suzuki, Hidenori Fujita, Shuichi Ohkubo, Yoshikazu Iwasawa. Discovery of TAS0953/HM06, a novel next generation RET-specific inhibitor capable of inhibiting RET solvent front mutations [abstract]. In: Proceedings of the AACR-NCI-EORTC Virtual International Conference on Molecular Targets and Cancer Therapeutics; 2021 Oct 7-10. Philadelphia (PA): AACR; Mol Cancer Ther 2021;20(12 Suppl):Abstract nr P06-02.

Identification of RET fusions in a Chinese multicancer retrospective analysis by next-generation sequencing.

Fusion of RET with different partner genes has been detected in papillary thyroid, lung, colorectal, pancreatic, and breast cancer. Approval of selpercatinib for treatment of lung and thyroid cancer with RET gene mutations or fusions calls for studies to explore RET fusion partners and their eligibility for RET‐based targeted therapy. In this study, RET fusion patterns in a large group of Chinese cancer patients covering several cancer types were identified using next‑generation sequencing. A total of 44 fusion patterns were identified in the study cohort with KIF5B, CCDC6, and ERC1 being the most common RET fusion partners. Notably, 17 novel fusions were first reported in this study. Prevalence of functional RET fusions was 1.05% in lung cancer, 6.03% in thyroid cancer, 0.39% in colorectal cancer, and less than 0.1% in gastric cancer and hepatocellular carcinoma. Analysis showed a preference for fusion partners in different tumor types, with KIF5B being the common type in lung cancer, CCDC6 in thyroid cancer, and NCOA4 in colorectal cancer. Co‐occurrence of EGFR mutations and RET fusions with rare partner genes (rather than KIF5B) in lung cancer patients was correlated with epidermal growth factor receptor‐tyrosine kinase inhibitor resistance and could predict response to targeted therapies. Findings from this study provide a guide to clinicians in determining tumors with specific fusion patterns as candidates for RET targeted therapies.

Extrapulmonary tuberculosis in patients with RET fusion-positive non-small cell lung cancer treated with pralsetinib: A Korean single-centre compassionate use experience

BackgroundPralsetinib, an RET inhibitor, has shown a dramatic response in patients with RET fusion- or mutation-positive tumours in previous studies. As a novel target agent, however, the safety of pralsetinib remains to be determined. Herein, we present two cases of extrapulmonary tuberculosis (TB) that developed during pralsetinib therapy. MethodsFrom April 2020, we administered pralsetinib to a total of 10 patients with RET fusion-positive non-small cell lung cancer under the compassionate use program. We retrospectively analysed the clinical efficacy of and adverse events related to pralsetinib therapy. ResultsOf the nine patients with measurable lesions, seven achieved a partial response. Additionally, one patient without measurable lesions also showed a clinical response. As of January 8, 2021, nine patients were still receiving pralsetinib therapy, while only one had discontinued pralsetinib therapy. Most adverse events were mild and manageable. However, two patients experienced extrapulmonary TB shortly after starting pralsetinib. The disease was well controlled with anti-TB medication, and the cancer lesions were managed through ongoing pralsetinib therapy. ConclusionThe development of TB during pralsetinib therapy is worth noting, although further large studies are required to demonstrate definitive relationship between causality and underlying mechanism.

WITHDRAWN: Unique genomic alterations of cerebrospinal fluid cell-free DNA are critical for targeted therapy of non-small cell lung cancer with leptomeningeal metastasis

We reported unique molecular features of cerebrospinal fluid (CSF) of NSCLC patients with leptomeningeal metastasis (LM), suggesting to establish CSF as a better liquid biopsy in clinical practices. We performed next-generation panel sequencing of primary tumor tissue, plasma and CSF from 131 NSCLC patients with LM, and observed high somatic copy number variations (CNV) in CSF of NSCLC patients with LM. The status of EGFR-activating mutations was highly concordant between CSF, plasma, and primary tumors. ALK translocation was detected in 8.3% of tumor tissues, but only 2.4% in CSF and 2.7% in plasma. Others such as ROS1 rearrangement, RET fusion, HER2 mutation, NTRK1 fusion, and BRAF V600E mutation were detected in 7.9% of CSF and 11.1% of tumor tissues, but only 4% in plasma. Our study has shed light on the unique genomic variations of CSF and demonstrated that CSF may represent better liquid biopsy for NSCLC patients with LM.

Clinical Outcomes of Diffuse Sclerosing Variant Papillary Thyroid Carcinoma in Pediatric Patients.

The diffuse sclerosing variant of papillary thyroid carcinoma (DSV) may be more aggressive than conventional well-differentiated non-DSV related papillary thyroid carcinomas (N-PTC). Retrospective chart review. Retrospective review of clinical outcomes for patients 21 years of age or younger who underwent initial surgery for PTC at a single institution from January 1, 2005 to April 1, 2020. Genomic analysis was performed using targeted next-generation sequencing. Data were analyzed using Fischer's exact test and Kaplan-Meier curve log-rank test. Our cohort consisted of 72 patients, nine with DSV and 63 with N-PTC. Age at diagnosis was comparable (15.4 vs. 16.2 years, respectively, P=.46). DSV were more likely to be in the high-risk American Thyroid Academy pediatric risk group (100% vs. 41.3%, P=.004), to present with regional cervical lymph node metastases (100% vs. 60.3%, P=.036), and to present with distant metastases (67% vs. 22%, P=.005). No mortality seen in either group over 27.5 (interquartile range 14.8, 46.00) months average follow-up. Throughout the follow-up period, DSV were more likely to experience progression than N-PTC (hazard ratio=5.7 [95% confidence interval 1.7-20.0; P=.0056]). In a subset of 19 patients with aggressive disease who had molecular testing as part of clinical care we detected RET fusions in nearly all DSV compared to a minority of N-PTC (83% vs. 15.4%, P=.0095). Pediatric patients with DSV have more advanced disease at diagnosis and are more likely to experience progression of disease compared to patients with N-PTC. The prevalence of RET fusions in our cohort recapitulates the frequency of this alteration described in prior studies. 4 Laryngoscope, 132:1132-1138, 2022.

Outcomes of BRAF, MET, RET, and ROS1 Mutated Non-Small Cell Lung Cancer With Brain Metastases (NSCLCBM)

Lung cancer is the leading cause of cancer-related deaths worldwide. Non-small cell lung cancer (NSCLC) also accounts for the highest number of brain metastases. Recent advances have been made from standard platinum-based chemotherapy to gene-directed therapies. EGFR and ALK mutations are the most well-studied directed therapies. However, newer targets in NSCLC are being studied, including BRAF mutations, MET exon skipping, RET fusions, and ROS1 rearrangements. In this retrospective study, we evaluated overall survival (OS) and progression-free survival (PFS) in NSCLCBM patients with BRAF, MET, RET, and ROS1 gene mutations.NSCLCBM patients diagnosed between 2010 and 2019 at our tertiary care center were investigated. Molecular marker status, systemic therapies, and date of progression were collected for each patient. We defined OS as the date of diagnosis of brain metastases to the date of last follow-up or death. The Cox proportional model was used to estimate OS and PFS.2989 NSCLCBM patients were detected, 18 had a BRAF mutant, 12 had MET exon skipping, 4 had RET fusion, and 6 had ROS1 rearrangement. The median OS (mOS) in patients who were BRAF positive was 101.7 months, ALK positive was 97.7 months, RET positive was 49.3 months, and ROS1 positive was 50.8 months. The median PFS (mPFS) for BRAF, MET, RET, and ROS1 was 99.2 months, 97.7 months, 31.6 months, and 40.6 months, respectively.Molecular mutations continue to be a topic of great interest in the field of NSCLCBM. These molecular mutations function as both prognostic predictors and druggable targets. Our retrospective study showed improved mPFS in patients with BRAF and MET mutations when compared to RET and ROS mutated patients and improved mOS in patients with MET mutations when compared to patients with RET mutations. However, due to the small sample size and the fact that these mutations are not mutually exclusive, it is difficult to determine statistical significance. Further studies need to be completed with larger sample sizes to determine outcomes in isolated mutations.

Phase 1 multicenter study of the HSP90 inhibitor SNX-5422 plus carboplatin and paclitaxel in patients with lung cancers

ObjectivesSingle-agent heat shock protein 90 (HSP90) inhibition has demonstrated activity in oncogene-driven non-small cell and small cell lung cancers. SNX-5422 is an oral HSP90 inhibitor with increased activity in vitro with the addition of carboplatin and paclitaxel. Therefore, we conducted a phase 1, open-label, multicenter study to evaluate SNX-5422, carboplatin and paclitaxel followed by SNX-5422 maintenance in patients with advanced lung cancers. Materials and methodsIn part 1 (3 + 3 dose escalation), SNX-5422 (50/75/100-mg/m2) was dosed every other day (qod) for 21 days (28-day cycle) for ≤4 cycles; carboplatin (AUC 5)-paclitaxel (175 mg/m2) was administered once every 3 weeks for ≤6 courses. In part 2 (maintenance), subjects who achieved at least stable disease in part 1 received 100 mg/m2 SNX-5422 monotherapy qod for 21 days (28-day cycle). ResultsTwenty-three patients with advanced non-small cell lung cancer (NSCLC, n = 20) and small cell lung cancer (SCLC, n = 3) were enrolled. The median age was 60 years and 61% (n = 14/23) had ≥1 prior treatment regimens. The maximum tolerated dose of SNX-5422 was 100 mg/m2 qod in combination with carboplatin-paclitaxel. The most common treatment-related grade 3/4 adverse events (part 1/part 2) were diarrhea (26%/15%) and nausea (9%/0%). In response-evaluable patients with NSCLC, 33% (6/18) had a partial response, 56% (10/18) stable disease, and 11% (2/18) progressive disease. Patients who remained on single-agent SNX-5422 maintenance therapy ≥2 months (n = 9) had cancers enriched for oncogenic drivers (n = 3 KRAS mutation, n = 1 EGFR exon 20 mutation, n = 1 HER2 mutation, and n = 1 RET fusion). ConclusionsThe triplet combination of SNX-5422, carboplatin and paclitaxel followed by maintenance SNX-5422 therapy was well-tolerated and showed anti-tumor activity. Cancers for which disease control on single-agent SNX-5422 maintenance was observed were enriched for oncogene-driven NSCLCs.

Unique Genomic Alterations of Cerebrospinal Fluid Cell-Free DNA Are Critical for Targeted Therapy of Non-Small Cell Lung Cancer With Leptomeningeal Metastasis.

We reported unique molecular features of cerebrospinal fluid (CSF) of nonsmall cell lung cancer (NSCLC) patients with leptomeningeal metastasis (LM), suggesting establishing CSF as a better liquid biopsy in clinical practices. We performed next-generation panel sequencing of primary tumor tissue, plasma, and CSF from 131 NSCLC patients with LM and observed high somatic copy number variations (CNV) in CSF of NSCLC patients with LM. The status of EGFR-activating mutations was highly concordant between CSF, plasma, and primary tumors. ALK translocation was detected in 8.3% of tumor tissues but only 2.4% in CSF and 2.7% in plasma. Others such as ROS1 rearrangement, RET fusion, HER2 mutation, NTRK1 fusion, and BRAF V600E mutation were detected in 7.9% of CSF and 11.1% of tumor tissues but only 4% in plasma. Our study has shed light on the unique genomic variations of CSF and demonstrated that CSF might represent better liquid biopsy for NSCLC patients with LM.

MA02.02 Efficacy and Safety of Pralsetinib in Chinese Patients with Advanced RET Fusion+ Non-Small Cell Lung Cancer

RET fusion has been identified as an oncogenic driver in approximately 1-2% of patients with NSCLC. Pralsetinib is a highly potent and selective inhibitor of RET and oncogenic RET alterations. ARROW is a phase I/II, open-label, and first-in-human study to evaluate the safety and antineoplastic activity of pralsetinib in a variety of advanced RET altered solid tumors including NSCLC. Previously we reported the efficacy and safety results of pralsetinib in a cohort of Chinese patients with RET fusion+ NSCLC after platinum-based chemotherapy at WCLC 2020.