RET Fusion Research Articles

MA14.02 RET Fusion Testing in Advanced Non-Small Cell Lung Carcinoma Patients: the RETING Study

The approval of selective RET inhibitors for patients with advanced RET fusion positive non-small cell lung carcinoma (NSCLC) means that the importance of accurately identifying those patients has never been greater. Due to the co-existance of single-gene testing and next-generation sequencing (NGS), we hypothesized that a comparison of RET fusions testing assays is urgently needed. Along those lines, the performance of RET immunohistochemistry (IHC) and RET fluorescence in situ hybridization (FISH) has recently been challenged. Physicians across 17 hospitals contributed to identify patients with RET fusion positive NSCLC as part of routine clinical care. In addition, RET fusion negative samples from NSCLCs diagnosed at the referral institution were also included. All tumors underwent targeted RNA-based NGS (Oncomine Comprehensive Assay v3), break-apart RET FISH (Vysis) with an automated scanning system (BioView), and RET IHC (clone EPR2871, Abcam). The material available for all tumors had been formalin-fixed and paraffin-embedded. Only cases with enough tissue available (i.e. a minimum of 50 tumor cells, as per FISH test requirements) and sufficient sequencing coverage after NGS were included. FISH and IHC results were interpreted by using previously described criteria. The NGS result was used as the gold-standard. Analyses by the three assays was succesful in all 80 tumors. Thirty-seven RET-positive samples and 43 RET-negative NSCLCs were identified. Signet ring cells and psammomatous calcifications were frequently observed in RET-positive samples (in 30% and 27% of tumors, respectively). The most common partners were KIF5B (29/37, 78%), followed by CCDC6 (6/37, 16%). Other partners included NCOA4 (1/37, 3%) and AKAP13 (1/37, 3%). Thirty-five out of the 37 (95%) NGS-positive samples were FISH-positive (86% with a split pattern and the remaining 14% with a single 3’ signal pattern). Six of those FISH-positive cases (6/35, 17%) displayed very challenging split signals (≤2 signal diameter). The two FISH-negative samples were KIF5B-RET variants that showed a narrow split (≤1 signal diameter) in 36% and 38% of tumor cells, respectively. All 43 NGS-negative tumors were also FISH-negative. Regarding RET IHC, all NGS-positive cases showed cytoplasmic staining with a mean H-score of 210 (median 210, range 5-300). Within the NGS-negative cohort, cytoplasmic staining was observed in 8 cases (19%), with a mean H-score of 9 (median 0, range 0-150). Interestingly, the two RET FISH-negative but NGS-positive samples showed relevant IHC positivity (H-score of 165 and 255, respectively). The most frequent partner in this large multicenter series of RET fusion positive NSCLCs was KIF5B. The concordance between RNA-based NGS and FISH was high, with 0% failure rate. However, the interpretation of RET FISH is very challenging due to the frequent occurrence of narrow split signals (22% in this series). RET IHC should be investigated further as an alternative method to resolve an equivocal FISH or NGS result. Funding This study was mainly funded by Lilly. We also thank Instituto de Salud Carlos III (ISCIII) (Fondos FEDER and Plan Estatal I+D+I 2008–2011 [PI11/02866] and 2013–2016 [PI14-01176 y PI17-01001]) and the iLUNG Program (B2017/BMD-3884) from the Comunidad de Madrid.

Biomarker testing patterns in patients with stage IV non-small cell lung cancer (NSCLC) in U.S. community-based oncology practice setting.

300 Background: This study evaluated rates of biomarker testing for patients with stage IV non-squamous NSCLC, which is known to have a ̃40% biomarker-positive rate (AMP, 2020), in a community-based oncology practice setting in the United States (US). Methods: A retrospective study was performed using data from a US electronic medical record database of patients aged ≥18 years with an initial diagnosis (index dx) of stage IV non-squamous NSCLC between Jan 1, 2015 and Dec 31, 2019. Unstructured data on molecular biomarker testing (single-gene and next-generation sequencing [NGS]-based) were abstracted from patient charts utilizing Natural Language Processing for EGFR mutation, ALK rearrangement, BRAF mutation, ROS1 rearrangement, MET exon14 mutation, RET fusion, NTRK fusion, and PD-L1 expression. Systemic therapy was obtained from structured data. Data were summarized using descriptive statistics. This study received a waiver of consent from Advarra IRB. Results: Of 646 patients identified in the database, 500 met all inclusion criteria and are included in this analysis. The majority (73.8%) were diagnosed in 2018 (n = 162; 32.4%) and 2019 (n = 207; 41.4%). Mean age (SD) was 70.0 (10.1) years, with 53.2% female. A total of 447 (89.4%) were tested for at least one biomarker after index diagnosis of which 81.2% (n = 406) had at least one single-gene test; 54.8% (n = 274) had an NGS test and 66.8% were tested for PD-L1. Single-gene or NGS-based testing was > 85% of patients across all index years. The use of NGS-based tests ranged from 35.0% among patients whose first diagnosis was in 2015 to 59.4% in 2019. Overall, 85.4% (n = 427) of the cohort received first-line treatment with chemotherapy (53.6%), immunotherapy (48.2%), or targeted therapy (14.2%). Among patients who received biomarker tests, 15.4% received targeted treatment and 49.7% received immunotherapy treatment, including checkpoint inhibitors, during first-line treatment. Conclusions: NGS testing utilization increased during the study period and by 2019, 59% of patients received NGS-based testing. Opportunities persist for practices to improve testing and achieve guideline recommendations. PD-L1 biomarker testing was performed amongst the highest proportion of patients in this study and nearly 50% of all patients received immunotherapy, including checkpoint inhibitors. Targeted therapy was used in 14.2% of this population, suggesting that patients with actionable biomarkers may not be receiving targeted treatment for their disease, potentially due to gaps in testing among patients in this dataset.

P60.09 Real-World Readiness of US Laboratories to Test Metastatic NSCLC Patients for Rare Actionable Genomic Variants by NGS

Various rare driver genomic variants have been investigated in metastatic non-squamous non-small cell lung cancer (mNSCLC). Individually they are considered rare (<3% prevalence), however, studies have shown collectively they represent up to 14.5% of the mNSCLC mutation profile. While multiple targeted therapies for rare variants such as NTRK fusions, MET exon14 skipping and RET fusions have been approved in the US for 1st line therapy in mNSCLC, other variants such as HER2 exon20ins, EGFR exon20ins, and FGFR-alterations are also gaining traction.

P01.01 LIBRETTO-432: A Placebo-Controlled Phase 3 Study of Adjuvant Selpercatinib in Stage IB-IIIA RET Fusion-Positive NSCLC

Approximately 30% of patients diagnosed with NSCLC present with early-stage (IB-IIIA) disease. Standard treatment options for these patients are definitive locoregional therapies with/without adjuvant chemotherapy, followed by surveillance until disease recurrence. While targeted therapies are standard treatment for metastatic NSCLC with driver mutations, their use in the early-stage setting is still being characterized. Selpercatinib, a highly selective, potent and CNS active RET inhibitor, demonstrated robust and sustained antitumor activity with manageable toxicity in patients with RET fusion-positive advanced NSCLC. There is a growing evidence demonstrating that oncogene addiction in NSCLC could be actionable regardless of disease stage. LIBRETTO-432 is a Phase 3, global, multicenter, randomized, double-blind, controlled trial evaluating the efficacy and safety of adjuvant selpercatinib versus placebo in patients with RET fusion-positive Stage IB-IIIA NSCLC following completion of definitive radiotherapy or surgery with a curative intent, and other adjuvant therapy if indicated (NCT04819100). Patients (n≈170) will be randomized (1:1) to Arm A (selpercatinib twice daily [160mg ≥50kg; 120mg <50kg]), or B (placebo), in continuous 28-day cycles for a maximum treatment duration of 3 years (Figure 1). Stratification factors include disease stage (Stage IB/II/IIIA) and prior definitive therapy (surgery, radiotherapy). Crossover is allowed for Arm B patients who experience disease recurrence. Treatment will continue until disease recurrence, unacceptable toxicity, withdrawal, or death. Key eligibility criteria include age ≥18 years; histologically confirmed Stage IB/II/IIIA NSCLC; mandatory brain MRI during screening to rule out metastasis; presence of activating RET fusion in tumor by PCR/NGS (local or central testing); received definitive locoregional therapy with curative intent (surgery, radiotherapy) for Stage IB/II/IIIA NSCLC; and ECOG performance status 0-1. Maximum time allowed between definitive therapy completion and randomization must be within 26 weeks. Key exclusion criteria are presence of other known oncogenic drivers; evidence of SCLC; and evidence of disease recurrence following definitive therapy. The primary endpoint is investigator-assessed event-free survival (EFS) in the primary analysis population. EFS is defined as time from randomization until locoregional disease recurrence with histopathological confirmation, distant disease recurrence per RECIST v1.1 or histopathological confirmation, or death. Gated secondary endpoints include investigator-assessed EFS in the overall population and overall survival in both the primary analysis and overall population. Non-gated secondary efficacy endpoints include blinded independent central review (BICR)-assessed EFS, time to distant disease recurrence in the CNS assessed by investigator and BICR, and progression-free survival on the next line of treatment. ▪▪▪ ▪▪▪

Cytomorphologic features of intraductal salivary gland carcinoma: A multi-institutional study of 13 FNA cases with histologic, molecular, and clinical correlations.

Intraductal carcinoma of the salivary gland (IDC) is a rare cancer with potential actionable targets, including RET fusions. Histologic and molecular features of IDC were recently reported, but cytomorphologic data are limited. In the largest multi-institutional fine-needle aspiration (FNA) series, the authors describe the cytomorphologic features of 13 IDC cases with available clinical, radiologic, histopathologic, and molecular data. The cases included 13 FNAs for 9 low-grade (LG) IDCs and 4 high-grade (HG) IDCs with corresponding histopathology and available molecular, imaging, and clinical data. Smears and liquid-based preparations available for 12 FNAs were semiquantitatively scored for key cytomorphologic findings and correlated with the corresponding resection. LG IDC FNAs showed a cellular, biphasic population of large, atypical ductal cells with mildly pleomorphic nuclei in a clean background and a minor population of small, uniform myoepithelial cells. In contrast, all HG IDC FNAs showed predominantly ductal cells with marked nuclear pleomorphism, coarse chromatin, and necrosis. With the Milan system, most LG and HG IDC FNAs were classified as either salivary gland neoplasms of uncertain malignant potential (54%) or malignant (31%). Immunohistochemistry showed ductal epithelial reactivity with mammaglobin, androgen receptor, and S100, whereas myoepithelial cells were positive for p63 and/or calponin. Among cases with next-generation sequencing, 4 LG IDCs showed NCOA4-RET gene fusions, whereas an HG IDC showed HRAS and PIK3CA mutations. The cytomorphology of IDC overlaps with other benign and malignant salivary gland neoplasms. Immunohistochemistry limits the differential diagnosis, but definitive classification requires molecular analysis. A diagnosis of IDC has potential implications for patient management.

Programmed death-ligand 1 expression and its associations with clinicopathological features, prognosis, and driver oncogene alterations in surgically resected lung adenocarcinoma

ObjectivesProgrammed death-ligand 1 (PD-L1) expression is a predictive biomarker of response to immunotherapies targeting programmed death-1/PD-L1 in advanced-stage lung adenocarcinoma. The aim of this study was to investigate the associations between PD-L1 expression and clinicopathological features, prognosis, and driver oncogene alterations in patients with lung adenocarcinoma. Materials and methodsWe evaluated PD-L1 expression in 1,005 surgically resected lung adenocarcinoma specimens, by immunohistochemistry using the 22C3 antibody. PD-L1 positivity was defined based on the proportion of stained tumor cells (TPS) on tissue microarrays: <1% (negative), 1–49% (weakly positive), and ≥ 50% (strongly positive). Correlations between PD-L1 expression and clinicopathological features, prognosis, and driver oncogene (EGFR, KRAS, ALK, ROS1, and RET) alterations in lung adenocarcinoma were analyzed. ResultsPD-L1 expression was negative in 726 (72%) of 1,005 tumors, weakly positive in 161 (16%), and strongly positive in 118 (12%). Male sex, smoking, elevated serum carcinoembryonic antigen levels, advanced pathological stages, high-grade tumors, predominantly solid tumors, tumors with lymphatic permeation or vascular or pleural invasion, tumors without EGFR mutations, and tumors with KRAS mutations were more common in patients with PD-L1-positive tumors (TPS ≥ 1%) than in those with PD-L1-negative tumors (TPS < 1%). PD-L1 positivity was not associated with ALK, ROS1, or RET fusion status. Although PD-L1 positivity was associated with poor overall survival and poor relapse-free survival in all patients, this was not statistically significant after adjusting for prognostic factors in the multivariate analysis. In the subgroup analysis according to driver oncogene alterations, PD-L1 positivity was associated with poor relapse-free survival only in patients with EGFR-mutated tumors. ConclusionSurgically resected lung adenocarcinomas with increased PD-L1 expression were biologically aggressive tumors that frequently occurred in male smokers. PD-L1 expression and its prognostic significance differed according to driver oncogene alterations.

1148P Identification and validation of RET fusions in lung adenocarcinoma through DNA and RNA sequencing

RET fusion has emerged as a targetable oncogenic driver in non-small cell lung cancer. The optimal methods to identify actionable RET fusions during clinical practice remain to be evaluated. Herein, we performed a comparative analysis on RET fusions using targeted next-generation sequencing at DNA (DNA-seq) and RNA (RNA-seq) levels.

RET Inhibitors in Non-Small-Cell Lung Cancer.

Simple SummaryNon-small cell lung cancer (NSCLC) remains a significant cause of death worldwide, despite the significant progresses to date. Multiple molecular alterations have been identified in NSCLC, leading to the development of target-based agents that have shown significant clinical benefits. Rearranged during Transfection (RET) fusions have recently emerged as a new potential target and a number of non-selective and selective RET inhibitors have been tested in RET positive NSCLC. In this review we analyse and summarise the characteristics of RET functions and its alterations in NSCLC. We then present the state of the art RET inhibitors in the treatment of NSCLC, discussing the ongoing trials and the future perspectives for RET positive (RET+) NSCLC patients.RET rearrangements are observed in 1–2% of non-small-cell lung cancer (NSCLC) patients and result in the constitutive activation of downstream pathways normally implied in cell proliferation, growth, differentiation and survival. In NSCLC patients, RET rearrangements have been associated with a history of non-smoking, a higher rate of brain metastasis at initial diagnosis and a low immune infiltrate. Traditionally, RET fusions are considered mutually exclusive with other oncogenic drivers, even though a co-occurrence with EGFR mutations and MET amplifications has been observed. Cabozantinib, vandetanib and lenvatinib are the first multi-kinase inhibitors tested in RET-rearranged NSCLC patients with contrasting results. More recently, two selective RET inhibitors, selpercatinib and pralsetinib, demonstrated higher efficacy rates and good tolerability and they were approved for the treatment of patients with metastatic RET fusion-positive NSCLC on the bases of the results of phase II studies. Two ongoing phase III clinical trials are currently comparing selpercatinib or pralsetinib to standard first line treatments and will definitively establish their efficacy in RET-positive NSCLC patients.

1753P REarranged during Transfection [RET] gene fusion testing patterns for patients [pts] with papillary thyroid cancer [PTC] across five European countries

RET fusions occur in 10-20% of pts with PTC. RET fusion testing enables identification of pts who may benefit from targeted treatments [tx]. This study described real-world RET fusion testing patterns for pts with PTC in France [FR], Germany [DE], Italy [IT], Spain [ES] and the UK.

Targeted Therapy for RET Fusion Lung Cancer: Breakthrough and Unresolved Issue.

Molecular drugs targeting mutated or rearranged oncogene drivers have become one of the standard recognized treatments in patients with advanced and recurrent non-small cell lung cancer. RET is located in the long arm of human chromosome 10 and encodes a receptor tyrosine kinase protein, and RET fusion-positive lung adenocarcinoma occurs in 1%–2% of cases. Clinical trials of multikinase inhibitors, including cabozantinib, vandetanib, sorafenib, and lenvatinib, that inhibit RET oncogene activity have shown their antitumor efficacy. Recently, RET inhibitors such as pralsetinib and selpercatinib that are specialized for RET kinase have also been developed, and their efficacy was investigated in previous clinical trials (BLU-667 and LOXO-292). In this review, we summarized the effects and adverse events of multikinase and selective RET inhibitors and the various diagnostic techniques for RET gene fusion. In the perspective part, we focused on the unsolved issues on treatment for RET fusion-positive lung cancer and future developments.

Oncogene-specific differences in tumor mutational burden, PD-L1 expression, and outcomes from immunotherapy in non-small cell lung cancer

BackgroundNon-small cell lung cancer (NSCLC) patients bearing targetable oncogene alterations typically derive limited benefit from immune checkpoint blockade (ICB), which has been attributed to low tumor mutation burden (TMB) and/or...

High Prevalence of DICER1 Mutations and Low Frequency of Gene Fusions in Pediatric Follicular-Patterned Tumors of the Thyroid.

Follicular-patterned tumors of the thyroid in the adult population frequently harbor RAS mutations or PAX8-PPARG rearrangement, but little is known about molecular profiles in the pediatric patients with thyroid tumors, which is rare. To identify the molecular profile of pediatric follicular-patterned tumors, we enrolled 41 pediatric patients with follicular-patterned tumors from two institutions. We did next-generation sequencing using a mutation panel targeting 49 thyroid-tumor-related genes and a fusion panel targeting 88 types of thyroid-related gene fusions. We identified nonsynonymous mutations in at least one target gene in most of the tumors (28/41, 68%). Somatic DICER1 mutations (22%, n = 9) were the most common genetic alteration, followed by mutations of NRAS (15%), FGFR3 (15%), PTEN (12%), and STK11 (10%). Infrequent genetic alterations (≤ 5% of all cases) included mutations of HRAS, APC, TSHR, CTNNB1, TP53, EIF1AX, FGFR4, GNAS, RET, and SOS1, and gene fusion of THADA-IGF2BP3. DICER1 and RAS mutations were mutually exclusive. No patients had tumors related to the DICER1 syndrome or the Cowden syndrome. There was no significant difference in total mutation burden or distribution between follicular adenoma and follicular carcinoma. In the literature, the DICER1 mutation has been reported in 20 to 53% of pediatric patients with follicular-patterned tumors. In conclusion, our study reinforces the role of the DICER1 mutation in the development of pediatric thyroid tumors. Gene fusions rarely occur in pediatric follicular-patterned tumors. Mutation or gene fusion alone could not distinguish benign from malignant follicular-patterned tumors in pediatric patients.

Update on Superficial Spindle Cell Mesenchymal Tumors in Children.

The diagnosis of cutaneous and subcutaneous spindle cell neoplasms in children is often challenging and has potential therapeutic and prognostic implications. Although correctly diagnosing dermatofibrosarcoma protuberans and infantile fibrosarcoma is paramount, pathologists should not ignore a number of diagnostic pitfalls linked to mostly rare tumors with completely different clinical outcomes. In the last decade, a spectrum of novel entities has been described; information from molecular biology has helped to shape this new landscape for spindle cell tumors. Here, we review the most noteworthy neoplasms in this spectrum, with a focus on their histological similarities: fibroblastic connective tissue nevus, medallion-like dermal dendrocyte hamartoma, or plaque-like CD34-positive dermal fibroma, which share features with fibrous hamartoma of infancy; lipofibromatosis and lipofibromatosis-like neural tumor; and plexiform myofibroblastoma, a recently described neoplasm that should be distinguished from plexiform fibrohistiocytic tumor. These tumors also have genetic similarities, particularly gene rearrangements involving NTRK3 or NTRK1. These genetic features are not only essential for the differential diagnosis of infantile fibrosarcoma but are also of diagnostic value for lipofibromatosis-like neural tumors. The more recently described RET, RAF1, and BRAF gene fusions are also discussed.

Analytical Accuracy of RET Fusion Detection by Break-Apart Fluorescence In Situ Hybridization.

RET gene fusions are oncogenic drivers in nonsmall cell lung cancer and nonmedullary thyroid cancer. Selpercatinib (RETEVMO), a targeted inhibitor of RET, was approved by the US Food and Drug Administration for the treatment of RET fusion-positive nonsmall cell lung cancer and nonmedullary thyroid cancer emphasizing the need for rapid and accurate diagnosis of RET fusions. Fluorescence in situ hybridization (FISH) has been used to detect gene rearrangements, but its performance detecting RET rearrangements is understudied. To validate and describe the performance of Abbott Molecular RET break-apart FISH probes for detecting RET rearrangements. A training set with RET fusion-positive (13) and RET fusion-negative nonsmall cell lung cancer and nonmedullary thyroid cancer samples (12) was used to establish criteria for FISH scoring. The scoring criteria was then applied to a larger validation set of samples (96). A cutoff of 19% or more positive nuclei by FISH was established in the training set and determined by the mean ±3 SD. The validation set was tested using Abbott Molecular RET break-apart FISH compared with sequencing. With this cutoff, a sensitivity of 86% (12 of 14) and specificity of 99% (81 of 82) was achieved. Bootstrapping showed sensitivity could be optimized by using a greater than 13% cutoff with indeterminate samples of 13% to 18% abnormal nuclei requiring confirmation by an orthogonal method. Using this 3-tier scoring system sensitivity increased to 100% (14 of 14) and specificity was 96% (79 of 82). Abbott Molecular break-apart FISH probes can be used to detect RET fusions. Laboratories can optimize cutoffs and/or testing algorithms to maximize sensitivity and specificity to ensure appropriate patients receive effective, timely therapy.

Abstract 2215: Landscape of RET fusion identified by next-generation sequencing in a Chinese multi-cancer retrospective analysis

Abstract Background: Fusion of RET with several partner genes has been detected in papillary thyroid, lung, colorectal, pancreatic and breast cancers. FDA has approved Retevmo (Selpercatinib) for lung and thyroid cancers with RET gene mutations or fusions. Here we focused on the prevalence of RET fusions in a Multi-cancer cohort (besides lung and thyroid cancers) for patients (pts) whom might benefit from RET inhibitors in clinical development. Methods: Genomic profiling was performed on 12,888 lung cancer pts, 2,848 colorectal cancer pts, 1,785 liver cancer pts, 1,169 Gastric cancer pts and 232 thyroid cancer pts from Jan. 2017 to Dec. 2019 using next-generation sequencing (NGS), which covers all exons of RET and specific intron 7-11 containing the break points of fusions. The fusion patterns of RET were analyzed. Results: A total of 165 RET fusions were identified in approximately 0.86% (163/18,922) of this Chinese multi-cancer cohort. The RET fusion-positive rates were 1.05% (135/12,888) in lung cancer pts, 0.39% (11/2,848) in the colorectal cancer pts, 0.06% (1/1,785) in liver cancer pts, 0.09% (1/1,169) in the 1169 Gastric cancer pts and 6.03% (15/232) in the 232 thyroid cancer pts tested. The most common partners were KIF5B (62.04%) and CCDC6 (21.17%) in lung cancer, NCOA4 (45.45%) and CCDC6 (27.27%) in colorectal cancer, and CCDC6 (93.33%) and NCOA4 (6.67%) in thyroid cancer. The most frequent regions of RET fusions were intron 11 (140/165) and intron 10 (15/165). The common fusion partners detected in different cancers are variable, indicating that the same oncogene has different carcinogenic mechanisms in cancers, and the sensitivity of these fusions to RET inhibitors in different cancers needs to be further studied. Conclusions: This study revealed the molecular features of RET rearrangement in Chinese cancer pts, which might result in more effective personalized diagnoses and therapies. Citation Format: Ting Lei, Weiran Wang, Danhua Wang, Junfeng Fu, Yu Wang, Ze Wang, Zhe Fan, Zhenyang Lv, Tonghui Ma. Landscape of RET fusion identified by next-generation sequencing in a Chinese multi-cancer retrospective analysis [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 2215.

SY28-4 Clinical development of RET inhibitors for RET fusion positive non-small cell lung cancer (NSCLC)

RET gene rearrangements retaining the kinase domain are oncogenic drivers in NSCLC, papillary thyroid cancer, and multiple other cancers. In NSCLC, the most common RET fusion partners are KIF5B (most common) and CCDC6. The frequency of RET fusion positive NSCLC was reported 1-2% and, it was also 2% (182/8621, between Feb. 2013 and Oct. 2020) in the East Asian lung cancer genomic screening (LC-SCRUM-Asia). Base on the LC-SCRUM-Asia clinical genomic database, the patient characteristics were median age 61 (29-85) years, female 62%, never smoker 64% and adenocarcinoma 97%. Because RET fusion is thus an attractive therapeutic target in NSCLC, multikinase inhibitors with RET inhibitor activity, such as vandetanib and cabozantinib, have been evaluated in prospective clinical trials. A clinical study of vandetanib for RET fusion positive NSCLC (LURET study) was conducted in Japan and objective response rate (ORR) was 53% and median progression free survival was 4.7 months. However, as a result of the nonselective nature of these multikinase inhibitors, patients had off-target adverse effects, such as hypertension, rash, and diarrhea and this resulted in only limited clinical efficacy. In contrast, the recent discovery and clinical validation of highly potent selective RET inhibitors such as selpercatinib (LOXO-292) and pralsetinib (BLU-667) demonstrated improved efficacy and a more favorable toxicity profile. These drugs appear to have broad activity across tumors with activating RET alterations. In a phase I/II clinical trial of selpercatinib (LIBRETTO-001), ORR 64% in 105 previously treated RET fusion positive NSCLC and 85% in 39 previously untreated patients were observed. RET-selective inhibitors selpercatinib and pralsetinib demonstrated favorable antitumor activity and safety profiles in RET fusion positive advanced NSCLC, and both received approval by the US FDA for it. In addition, the mechanisms of resistance to selective RET inhibitors are currently investigated.

MO4-7 Efficacy and safety with selpercatinib in patients with RET fusion+ NSCLC: Analysis by last prior systemic therapy

MO4-7 Efficacy and safety with selpercatinib in patients with RET fusion+ NSCLC: Analysis by last prior systemic therapy

Abstract CT011: Efficacy and safety of selpercatinib in RET fusion-positive cancers other than lung or thyroid cancers

Abstract Introduction: Selpercatinib, a first-in-class highly selective and potent RET kinase inhibitor, is approved in multiple countries for the treatment of RET fusion-positive lung or thyroid cancers. RET fusions are also implicated in the pathogenesis of other cancers. Selpercatinib's efficacy and safety were thus explored in patients (pts) with RET fusion-positive non-lung/non-thyroid cancers in a global, multicenter, registrational trial. Methods: Adults with locally advanced or metastatic RET fusion-positive non-lung/non-thyroid solid tumors enrolled in the phase 1/2 LIBRETTO-001 trial (NCT03157128) were included in this analysis (data cut-off: 19 March 2021). Following dose escalation, pts received the recommended dose of 160 mg orally, twice daily. Pts enrolled long enough to allow 6-month follow-up from their first dose comprised the efficacy-evaluable population. Response was assessed (RECIST 1.1) by investigators. The primary endpoint was objective response rate (ORR). Secondary endpoints included duration of response (DoR), time to response, and safety. Results: Thirty-two pts with RET fusion-positive non-lung/non-thyroid cancers included 12 unique tumor types: 9 pancreatic, 9 colon, 2 each of breast, salivary, sarcoma, and unknown primary, and 1 each of carcinoid, rectal neuroendocrine, small intestine, xanthogranuloma, ovarian, and pulmonary carcinosarcoma. The median age was 48 years (range 22-85). Twenty-nine pts received prior systemic therapy (median prior lines: 2, range 0-9). The ORR was 47% (N=15/32, 95% CI: 29-65). Objective responses were observed in 9 unique cancer types including colon, pancreatic, carcinoid, small intestine, salivary, xanthogranuloma, breast, ovarian, and sarcoma, and 5 additional patients had stable disease lasting ≥ 16 weeks. Median time to response was 1.9 months (range 0.7-7.3). Median DoR was not reached (median follow-up time of 13 months). Responses were ongoing in 73% (11/15) of pts. Safety among this population was consistent with the overall selpercatinib safety database. No patients in this cohort discontinued due to treatment-related AEs. Conclusion: Selpercatinib demonstrated promising antitumor activity in RET fusion-positive non-lung/non-thyroid cancers, including multiple treatment-refractory GI malignancies. Broad-based genomic profiling is essential to identify actionable oncogenic drivers, including RET fusions. The safety and efficacy of selpercatinib will continue to be explored in pts with these cancers in the ongoing LIBRETTO-001 study. Citation Format: Vivek Subbiah, Bhavana Konda, Todd Bauer, Caroline McCoach, Gerald Falchook, Masayuki Takeda, Jyoti Patel, Jared Weiss, Nir Peled, Lyudmila Bazhenova, Victoria Soldatenkova, Pearl French, Nora Drove, Oliver Gautschi, Alexander Drilon. Efficacy and safety of selpercatinib in RET fusion-positive cancers other than lung or thyroid cancers [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 CT011.

Abstract 2313: The characteristics of ERBB2 exon 20 insertion in a large cohort of Chinese NSCLC patients

Abstract Background: ERBB2 mutations, especially exon 20 insertion (ERBB2ex20ins) had been extensively reported in NSCLC as classical driver factors. Previous researches indicate that NSCLC pts with ERBB2ex20ins are drug-resistant to afatinib, gefitinib and erlotinib. Up to now, approvals of targeted therapy of ERBB2ex20ins are still in process. Therefore, the objective of this study is to discover the features of ERBB2ex20ins in Chinese NSCLC patients, which could lead to more effective and personalized diagnosis and treatment. Methods: 20656 Chinese NSCLC cases who had undergone molecular profiling at a Clinical Laboratory Improvement Amendments (CLIA) certified genomics laboratory in China between January 2017 to May 2020 were screened for our study. Some patients' clinical characteristics and treatment history were retrieved from the database for further evaluation. Results: 11492 males and 9134 females were included in our cohort. ERBB2 gene mutation rate was 5.94% (1226/20656). Among them, 290 patients (1.4%), including 114 males and 176 females, harbored with ERBB2ex20ins, which include with p. Tyr772_Ala775dup (84.56%), p.Gly778_Pro780dup (10.74%), p.Ala775_Gly776insLeu(1.01%), p.Ala775_Gly776insVal(1.01%) and others(2.68%). Additionally, ERBB2ex20ins occurred more frequently in female patients (61% vs 39%, p&amp;lt;0.005, fisher exact test), and had a relatively young age (p&amp;lt;0.005, wilcoxon test) compared with others. Moreover co-variations of 290 pts are occurring with EGFR(4, 1.38%), KRAS(3, 1.03%), TP53(156, 53.79%), ERBB2 amp(21, 7.24%), MET amp (2, 0.69%), ALK amp (1, 0.34%) and RET fusion (1, 0.34%). Besides, a relatively lower TMB (p&amp;lt;0.005, wilcoxon test) is shown on the patients with ERBB2ex20ins. We followed up 5 patients with ERBB2ex20ins mutations, who were all insensitive to traditional radiotherapy and chemotherapy and had poor prognosis with short PFS (1.5-12.4 months) and short OS (3.9-13.7 months). Conclusion: Our results showed that the ERBB2ex20ins mutation tended to occur in younger, female patients. Additionally, ERBB2ex20ins mutated samples exhibited lower levels of TMB compared to wildtype tumors, which may not benefit from anti-PD1 treatment. We also found patients with ERBB2ex20ins mutation have been associated with short PFS and short OS. The detail mechanism of resistance and appropriate therapeutic strategies remain to be further study. Citation Format: Danhua Wang, Hongling Yuan, Honglin Zhu. The characteristics of ERBB2 exon 20 insertion in a large cohort of Chinese NSCLC patients [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 2313.

Abstract 469: Comprehensive, large scale analysis of ALK, ROS1, RET, NTRK1 and NRG1 transcripts in lung cancer reveals over-expressing, potentially targetable patients

Abstract Background: Fusion involving anaplastic lymphoma kinase (ALK), RET proto-oncogene (RET) or ROSproto-oncogene 1, receptor tyrosine kinase (ROS1), neurotrophic receptor tyrosine kinase 1 (NTRK1)and neuregulin 1 (NRG1) are present in lung cancer (LC) and represent important biomarkers fortargeted therapies. However, little is known about the RNA expression levels of some of these genesregardless of fusions. Methods: We used a custom nCounter panel (NanoString Technologies) designed to detect fusionsand mRNA expression levels of ALK, ROS1, RET, NTRK1 and NRG1 in formalin-fixed paraffin embedded(FFPE) samples. RNA was purified from lung cancer tumor samples and analyzed with the panel. Thecounts corresponding to the 3' probes were normalized using the geometrical mean of thehousekeeping genes and then added to evaluate total mRNA expression levels. Cut-off values for veryhigh expression levels were established as the average counts in all samples (s.) studied for each geneplus three times the standard deviation. Results: A total of 580 LC s. from two different institutions were retrospectively analyzed for ALK,ROS1, RET and NTRK1 mRNA levels. Very high levels of ALK mRNA were found in 76 s. (13%). Of them,69/76 were also positive for EML4-ALK fusions and 61/76 had adenocarcinoma histology (ADC). OneALK-translocated patient with a sample with low levels of ALK mRNA did not respond to therapy.Twenty-two s. (3.8%) showed very high levels of ROS1 mRNA and 17/22 were ADC. In contrast withALK, only 4/22 had a concomitant ROS1 fusion. Among the remaining 16 s. with very high levels ofROS1 mRNA, 11 were ALK or EGFR positive and two were wt for the more common lung ADC geneticalteration. Regarding RET, very high expression levels were found in 11 s. (2%), only one of themshowed a RET fusion. Among the remaining 10 s., 6 presented neuroendocrine features and only 2were ADC. Regarding NTRK1, 4 s. showed very high expression levels of mRNA and only one of themwas positive for NTRK1 translocation. Finally, 116 LC s were analyzed for NRG1; very high mRNA levelswere detected in 2 cases, none of them translocated. Conclusions: Very high expression of ALK mRNA in NSCLC is associated with EML4-ALK translocations.In contrast, a significant number of fusion negative patients show high ROS1, RET and NTRK1 mRNAvery high levels. Further research is warranted to determine the clinical relevance of this finding. Citation Format: Cristina Aguado, Cristina Teixido, Ana Gimenez Capitan, Elba Marin, Ruth Roman, Sonia Rodriguez, Irene Moya, Roxana Reyes, Nuria Viñolas, Santiago Viteri, Andres Aguilar, Rafael Rosell, Noemi Reguart, Miguel Angel Molina-Vila. Comprehensive, large scale analysis of ALK, ROS1, RET, NTRK1 and NRG1 transcripts in lung cancer reveals over-expressing, potentially targetable patients [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 469.