Rearranged During Transfection Fusion Research Articles

CCDC6-RET fusion protein regulates Ras/MAPK signaling through the fusion- GRB2-SHC1 signal niche

Rearranged during transfection (RET) rearrangement oncoprotein-mediated Ras/MAPK signaling cascade is constitutively activated in cancers. Here, we demonstrate a unique signal niche. The niche is a ternary complex based on the chimeric RET liquid-liquid phase separation. The complex comprises the rearranged kinase (RET fusion); the adaptor (GRB2), and the effector (SHC1). Together, they orchestrate the Ras/MAPK signal cascade, which is dependent on tyrosine kinase. CCDC6-RET fusion undergoes LLPS requiring its kinase domain and its fusion partner. The CCDC6-RET fusion LLPS promotes the autophosphorylation of RET fusion, with enhanced kinase activity, which is necessary for the formation of the signaling niche. Within the signal niche, the interactions among the constituent components are reinforced, and the signal transduction efficiency is amplified. The specific RET fusion-related signal niche elucidates the mechanism of the constitutive activation of the Ras/MAPK signaling pathway. Beyond just focusing on RET fusion itself, exploration of the ternary complex potentially unveils a promising avenue for devising therapeutic strategies aimed at treating RET fusion-driven diseases.

Targeting RET alterations in non-small cell lung cancer

Rearranged during transfection (RET) alterations, which lead to aberrant activation of the RET proto-oncogene, have been identified in various cancers. In non-small cell lung cancer (NSCLC), RET mutations often manifest as RET fusion genes and are observed in 1–2 % of patients with NSCLC. In recent years, selective RET inhibitors such as selpercatinib and pralsetinib, approved by the Food and Drug Administration (FDA) in 2020, have been part of the revolutionary changes in the treatment landscape for non-small cell lung cancer. While first-generation RET inhibitors have become part of the standard of care for RET-fusion positive NSCLC, a new challenge has emerged: acquired resistance to RET inhibitors. RET resistance is a complex phenomenon that can manifest as either on-target or off-target resistance. Numerous studies have been conducted to identify the mechanisms behind this resistance. This review provides an overview of the biology of RET in NSCLC, methods of RET testing, and a comprehensive analysis of the clinical outcomes associated with multikinase and selective RET inhibitors for NSCLC. Additionally, we will explore future perspectives for RET fusion-positive NSCLC, including ongoing trials and the challenges involved in overcoming resistance to RET inhibitors.

Primary Resistance to RET Inhibition in a RET Fusion-Positive Pancreatic Neuroendocrine Carcinoma.

We present a 54-year-old White male with a diagnosis of stage IV pancreatic neuroendocrine carcinoma. Next-generation sequencing of the tumor/blood identified a complex tumor genome, which included a rearranged during transfection (RET) gene fusion. The patient initially received cytotoxic chemotherapy with a significant radiographic response. After 4 cycles of chemotherapy, the patient was transitioned to a clinical trial using selpercatinib, a RET inhibitor, as maintenance therapy. Unfortunately, our patient developed progression of disease at the first treatment monitoring scan. Our patient suffered primary resistance to RET-targeted therapy. Proposed mechanisms of resistance include intrinsic resistance of the nuclear receptor co-activator 4-RET fusion to RET inhibition, the RET fusion representing a passenger alteration to another tumorigenic driver pathway and/or decreased efficacy of RET inhibition after platinum-based chemotherapy. Our patient's clinical course highlights the fact that "actionable" genomic alterations do not always equate to patient benefit.

Selpercatinib-induced hepatotoxicity: A rare case report

Abstract Introduction/Objective Selpercatinib (Retevmo) is a highly selective rearranged during transfection (RET) kinase inhibitor indicated for treatment of solid tumors with RET gene mutation or fusion, such as medullary thyroid carcinoma or non-small cell lung carcinoma. Among selpercatinib’s side effects, severe hepatotoxicity was only seen in 3% of the patients. Here we report a case of selpercatinib-induced hepatotoxicity, which has not been well characterized before. Methods/Case Report The patient was a 56-year-old female who had medullary thyroid carcinoma with RET M918T mutation (pT3aN1b) status post total thyroidectomy. Recurrence occurred and selpercatinib treatment was initiated. Then the patient complained of mouth sores, tongue sensitivity, and lower extremity cramping. The dosage was reduced to half. The magnetic resonance imaging on day 67 of selpercatinib treatment showed heterogeneous enhancement in the right hepatic lobe, compatible with parenchymal liver disease/hepatitis, trace perihepatic ascites, and mild splenomegaly. On day 71, liver function abnormalities were detected (ALK 315 IU/L, ALT 745 IU/L, AST 899 IU/L, total bilirubin 7.7 mg/dL). Workups including autoimmune hepatitis serology, viral hepatitis, or other infections were all negative. She had no history of other drug use. On day 72, a liver biopsy was performed that demonstrated mild to moderate portal lymphocyte-predominant mixed inflammation with interface activity. The lobules showed marked inflammation with hepatocyte disorganization, acidophil bodies, hepatocyte dropout, and rare lipogranulomas. Bile duct injury and patchy canalicular cholestasis were also noted. Trichrome stain showed focal bridging fibrosis. Overall, the histologic findings were acute and chronic hepatitis pattern injury, favor selpercatinib-induced hepatotoxicity. Selpercatinib was discontinued. All liver enzymes gradually returned to normal levels on day 169. Results (if a Case Study enter NA) NA Conclusion Our study suggests that screening patients for abnormal liver function tests prior to and monitoring periodically during selpercatinib treatment is necessary. Based on the severity of hepatotoxicity, withholding, reducing the dose, or permanently discontinuing selpercatinib is recommended.

Expert consensus on the diagnosis and treatment of RET gene fusion non-small cell lung cancer in China.

The rearranged during transfection (RET) gene is one of the receptor tyrosine kinases and cell-surface molecules responsible for transmitting signals that regulate cell growth and differentiation. In non-small cell lung cancer (NSCLC), RET fusion is a rare driver gene alteration associated with a poor prognosis. Fortunately, two selective RET inhibitors (sRETi), namely pralsetinib and selpercatinib, have been approved for treating RET fusion NSCLC due to their remarkable efficacy and safety profiles. These inhibitors have shown the ability to overcome resistance to multikinase inhibitors (MKIs). Furthermore, ongoing clinical trials are investigating several second-generation sRETis that are specifically designed to target solvent front mutations, which pose a challenge for first-generation sRETis. The effective screening of patients is the first crucial step in the clinical application of RET-targeted therapy. Currently, four methods are widely used for detecting gene rearrangements: next-generation sequencing (NGS), reverse transcription-polymerase chain reaction (RT-PCR), fluorescence in situ hybridization (FISH), and immunohistochemistry (IHC). Each of these methods has its advantages and limitations. To streamline the clinical workflow and improve diagnostic and treatment strategies for RET fusion NSCLC, our expert group has reached a consensus. Our objective is to maximize the clinical benefit for patients and promote standardized approaches to RET fusion screening and therapy.

Selpercatinib monotherapy in a Chinese patient with RET fusion/EGFR co-mutated nonsmall cell lung cancer from the Phase II LIBRETTO-321 study: a case report.

Rearranged during transfection (RET) fusions and epidermal growth factor receptor (EGFR) mutations are potent oncogenic drivers in patients with nonsmall cell lung cancer (NSCLC), but rarely co-exist. Concurrent RET/EGFR mutations have been reported in patients with NSCLC who develop resistance to EGFR tyrosine kinase inhibitors but are even less frequent in treatment-naïve patients. Consequently, there is no standard treatment for RET/EGFR-mutated NSCLC. We report a case of RET/EGFR mutant NSCLC successfully treated with the oral, potent, highly selective RET inhibitor selpercatinib (160 mg daily for 28-day cycles) in an ongoing phase II study in Chinese patients with NSCLC (LIBRETTO-321). The patient, a female nonsmoker, was diagnosed with de-novo left lung adenocarcinoma with neuroendocrine differentiation, and a RET fusion was detected by next-generation sequencing testing. The patient had two tumors in the pleura, a third in the subcarinal lymph node, and a nontarget tumor in the pleura. Pleural biopsy analysis confirmed a RET fusion KIF5B (K15;R12) and an EGFR exon 19 deletion. The patient achieved a partial response (PR) with selpercatinib (absence of target tumors in pleura and reduction in the size of lymph node tumor). The PR persisted for 14.7 months, with disease progression in the nontarget lesion in the pleura and a new lesion in the liver (the PR had persisted), resulting in the discontinuation of selpercatinib. The only notable adverse event was grade 3 elevated transaminase, that was effectively managed by dose reduction. These data may support the use of selpercatinib in patients with RET/EGFR co-mutated NSCLC.

First results from the RETgistry: A global consortium for the study of resistance to RET inhibition in RET-altered solid tumors.

9065 Background: Rearranged during transfection ( RET) gene alterations are the oncogenic driver in diverse tumor types, including RET fusions identified in 1-2% of non-small cell lung cancers (NSCLC). While RET-selective tyrosine kinase inhibitors (TKIs) selpercatinib and pralsetinib are effective, acquired drug resistance remains a challenge. Here, we report the initial results from the RETgistry, an international consortium aimed at elucidating mechanisms of resistance to RET TKIs across RET-altered solid tumors. Methods: This was a retrospective analysis performed across 16 institutions. Patients (pts) were eligible if they had advanced solid tumor harboring an oncogenic RET alteration, received ≥1 RET TKI with disease progression, and underwent resistant tumor or liquid biopsy for next-generation sequencing (NGS). Results: A total of 103 time-distinct biopsies (62 tissue, 30 plasma, 11 paired tissue/plasma) were included in analysis, obtained from 88 pts with progression on a RET-selective TKI [selpercatinib (n = 70), pralsetinib (n = 14), selpercatinib and pralsetinib sequentially (n = 4)]. Pts had the following tumor types: 72 NSCLC (69% KIF5B-RET, 21% CCDC6-RET, 10% other RET fusion), 13 medullary thyroid cancer (TC) (54% RET M918T, 46% other RET mutation), and 2 papillary and 1 anaplastic TC (all, RET fusion). Median age was 58 (range, 21-86); 48% were male with 89% never/light smokers. Median duration of RET TKI preceding biopsies [first-line, n = 32 (31%); second-line, n = 42 (41%); third-/greater-line, n = 29 (28%)] was 16.5 months (mos) (95% CI, 14.0-19.6); median PFS was 14.1 mos (95% CI, 9.3-17.0). Resistant biopsies were obtained at median 15.0 mos from TKI initiation (range, 1.8-58.8). Acquired RET mutations were detected in 14 (14%), most common being G810 substitutions in 12 (12%). Potential off-target resistance gene alterations identified in 43 cases (42%) included MET amplification (14%), BRAF V600E or fusion (2%), KRAS gain or mutation (5%), ERBB2 amplification (2%), EGFR amplification (3%), ROS1 fusion (1%), and activating PIK3CA mutation or PTEN loss (4%). No resistant lung cancer biopsy demonstrated small cell transformation. The duration of TKI therapy (HR 0.64, p = 0.11) or PFS (HR 0.75, p = 0.33) did not differ according to the presence of on-target vs off-target resistance. NGS analyses of pre-RET-selective TKI tumors (n = 92) revealed frequent co-occurring alterations in TP53 (29%) and CDKN2A/B (12%). Conclusions: On-target resistance to RET inhibition due to acquired RET mutations was less common than off-target resistance, identified in 14%. The majority of RET TKI resistance is mediated by off-target mechanisms such as bypass receptor tyrosine kinase activation. Further studies are warranted to enable the development of therapeutic strategies to address resistance in pts with RET-altered tumors. The RETgistry accrual and data analyses continue.

Response to Pralsetinib in Multi-Drug-Resistant Breast Cancer With CCDC6-RET Mutation.

Triple-negative breast cancers (TNBC) represent a pathological subtype of breast cancer, which are characterized by strong invasiveness, high metastasis rate, low survival rate, and poor prognosis, especially in patients who have developed resistance to multiline treatments. Here, we present a female patient with advanced TNBC who progressed despite multiple lines of treatments; next-generation sequencing (NGS) was used to find drug mutation targets, which revealed a coiled-coil domain-containing protein 6 (CCDC6)-rearranged during transfection (RET) gene fusion mutation. The patient was then given pralsetinib, and after one treatment cycle, a CT scan revealed partial remission and adequate tolerance to therapy. Pralsetinib (BLU-667) is a RET-selective protein tyrosine kinase inhibitor that can inhibit the phosphorylation of RET and downstream molecules as well as the proliferation of cells expressing RET gene mutations. This is the first case in the literature of metastatic TNBC with CCDC6-RET fusion treated with pralsetinib, an RET-specific antagonist. This case demonstrates the potential efficacy of pralsetinib in cases of TNBC with RET fusion mutations and suggests that NGS may reveal new opportunities and bring new therapeutic interventions to patients with refractory TNBC.

Highly sensitive droplet digital PCR for detection of RET fusion in papillary thyroid cancer

BackgroundThyroid cancer is the most frequent malignancy of the endocrine system, of which papillary thyroid cancer (PTC) is the predominant form with a rapid increasing incidence worldwide. Rearranged during transfection (RET) fusions are common genetic drivers of PTC and the potent RET inhibitor selpercatinib has been recently approved for treating advanced or metastatic RET fusion-positive thyroid cancer. In this study we aimed to develop a droplet digital PCR (ddPCR) system to accurately detect RET fusion in PTC samples.MethodsThe frequency and distribution of RET fusions in PTC were analyzed using genomic data of 402 PTC patients in The Cancer Genome Atlas (TCGA) database. To establish the ddPCR system for detecting CCDC6::RET fusion, a plasmid containing CCDC6::RET infusion fragment was constructed as standard template, the annealing temperature and concentrations of primers and probe were optimized. The analytical performance of ddPCR and quantitative reverse transcription PCR (qRT-PCR) were assessed in standard templates and tissue samples from 112 PTC patients. Sanger sequencing was performed in all the RET fusion-positive samples identified by ddPCR.ResultsRET fusions were observed in 25 (6.2%) of the 402 TCGA samples, and 15 (60%) of the RET fusion-positive patients had the CCDC6::RET fusion. Compared with qRT-PCR, the ddPCR method showed a lower limit of detection (128.0 and 430.7 copies/reaction for ddPCR and qRT-PCR, respectively). When applying the two methods to 112 tissue samples of PTC, eleven (9.8%) CCDC6::RET fusion-positive samples were detected by qRT-PCR, while ddPCR identified 4 additional positive samples (15/112, 13.4%). All the CCDC6::RET fusion-positive cases identified by ddPCR were confirmed by Sanger sequencing except for one case with 0.14 copies/uL of the fusion.ConclusionThe accurate and sensitive ddPCR method reported here is powerful to detection CCDC6::RET fusion in PTC samples, application of this method would benefit more RET fusion-positive patients in the clinic.

Abstract 3419: TY-1091, a highly selective and potent second-generation RET inhibitor, demonstrates superior antitumor activity in multiple RET-mutant models

Abstract Proto-oncoprotein RET (rearranged during transfection) is a receptor tyrosine kinase and belongs to the cadherin superfamily. RET fusion proteins and gatekeeper mutations represent strong cancer drivers involved in the development of a variety of cancers. Although selective RET inhibitors selpercatinib (LOXO-292) and pralsetinib (BLU667) were recently marketed for patients with RET-dependent NSCLC and thyroid cancers, RET solvent front mutations G810R/S/C/V and other secondary mutations such as Y806C/N and V728A have been identified as mechanisms counting for acquired resistance to the two drugs and limits the applications of the kinase inhibitors. To provide novel RET inhibitors effective to a broader spectrum of RET fusions and mutations, we identified TY-1091 as a novel next-generation RET inhibitor through the in-house RET program and systemic screening of RET compound candidates. TY-1091 was characterized for its anti-tumor activity through in vitro and in vivo testing of a variety of RET-dependent tumor models including a panel of 17 engineered RET mutant Ba/F3 cell lines and 2 cancer cell models. The results show that TY-1091 inhibits wild type and major RET mutants (IC50, nM): RET G810S (9.5 nM), RET V804M/L/E (2.8-12.6 nM), and double mutants RET V804M/G810S (23.5 nM) and M918T/G810S (47.0 nM) through a biochemical screening against a panel of 17 engineered RET mutant Ba/F3 cell lines. Importantly, the inhibitory activity of TY-1091 is much higher than that of first-generation RET inhibitor Cabozantinib, and comparable to other second-generation compounds LOXO-292 and BLU-667. Consistent with its mode of action, TY-1091 grants extraordinary inhibition effects to tumor cell proliferation compared to its peer compounds LOXO-292 and BLU-667 (including TT (thyroid cancer, RET C634W) and LC2/ad (NSCLC, CCDC6-RET)), and the inhibition of the RET pathway activation, i.e., inhibition of RET phosphorylation (IC50 < 1 nM), SHC phosphorylation (IC50 = 4.6 nM) and ERK phosphorylation (IC50 = 9.8 nM) in Ba/F3-KIF5B-RET cells further validated the above in vitro phenotype. The therapeutic potential of TY-1091 was then further validated through mouse pharmacology in that TY-1091 demonstrated remarkable anti-tumor efficacy in a variety of xenograft models including Ba/F3 KIF5B-RET (wt), Ba/F3 KIF5B-RET (V804L), TT (thyroid cancer, RET C634W), and LC2/ad (NSCLC, CCDC6-RET). Detailed data will be presented. In summary, TY-1091 is a highly potent, orally available, and safe small molecule inhibitor to pan-RET mutations in cancer, and may attenuate SFMs-mediated resistance to existing RET therapy. The IND clearance from the US FDA was received and Phase I clinical investigations of TY-1091 shall be launched in the US soon. *To Whom Correspondence should be addressed to: Jun Li, Chengshan Niu and Yusheng Wu Citation Format: Chengshan Niu, Maolin Zheng, Huan Wang, Kaige Ji, Meihua Li, Guohui Wang, Rongzhen Ni, Apeng Liang, Aishen Gong, Yazhen Zhang, Hui Su, Mingyu Jiang, Shaoqing Chen, Xiugui Chen, Jun Li, Yusheng Wu. TY-1091, a highly selective and potent second-generation RET inhibitor, demonstrates superior antitumor activity in multiple RET-mutant models [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 3419.

Advances in the Diagnosis and Treatment of a Driving Target: RET Rearrangements in non-Small-Cell Lung Cancer (NSCLC) Especially in China.

In the era of precision medicine, with the deepening of the research on malignant tumor driving genes, clinical oncology has fully entered the era of targeted therapy. For non-small-cell lung cancer (NSCLC), the development of targeted drugs targeting driver genes, such as epidermal growth factor receptor (EGFR) and anaplastic lymphoma kinase (ALK), has successfully opened up a new model of targeted therapy. At present, proto-oncogene rearranged during transfection (RET) fusion gene is an important novel oncogenic driving target, and specific receptor tyrosine kinase inhibitors (TKIs) targeting RET fusion have been approved. This article will review the latest research about the molecular characteristics, pathogenesis, detection, and clinical treatment strategies of RET rearrangements especially in China.

389P Updated efficacy and safety of pralsetinib in Chinese patients with advanced RET fusion+ non-small cell lung cancer

Pralsetinib is a potent, selective Rearranged during Transfection (RET) inhibitor targeting oncogenic RET alterations and is the first RET inhibitor approved in China. ARROW is a global phase I/II registrational study to evaluate the safety and efficacy of pralsetinib in a variety of advanced RET altered solid tumors including non-small cell lung cancer (NSCLC). Here we present updated results of the ARROW study in Chinese patients with advanced RET fusion+ NSCLC.

Pralsetinib (Gavreto)


 CADTH recommends that Gavreto be reimbursed by public drug plans for the treatment of adult patients with rearranged during transfection (RET) fusion–positive locally advanced unresectable or metastatic non–small cell lung cancer (NSCLC) if certain conditions are met.
 Gavreto should only be covered to treat adult patients aged 18 years and older with locally advanced unresectable or metastatic RET fusion–positive NSCLC who have never received cancer treatment or who have received cancer treatment. Patients receiving Gavreto should be in relatively good health (i.e., have a good performance status as determined by a specialist) and not have cancer that has spread to the brain or if it has spread to the brain, is controlled.
 Gavreto should only be reimbursed if prescribed by a clinician with expertise in the management of NSCLC and if the cost of Gavreto is reduced. Gavreto should not be reimbursed in combination with other cancer treatment.

Abstract 403: Analysis of RET solvent front mutations shows an effect on protein activity in tumor cells

Abstract The rearranged during transfection (RET) gene encodes a receptor tyrosine kinase that is involved in the activation of several signal transduction pathways. Various RET fusions and point mutations were shown to play a role as oncogene drivers in different cancers. In 2020, two selective RET tyrosine kinase inhibitors (TKIs), pralsetinib and selpercatinib, were approved by the FDA for treatment of RET fusion-positive non-small cell lung cancer, RET-mutant medullary thyroid cancer and RET fusion-positive thyroid cancer. These drugs demonstrate a significant advance in efficacy and safety over previous, multi-targeted TKIs for the treatment of RET-positive patients. However, development of acquired resistance to these agents has been observed through the appearance of on-target secondary solvent front mutations in the RET G810 residue. Moreover, 5 different types of amino acid changes - G810A/C/R/S/V have been identified in this position, of which G810C, G810R and G810S are better characterized but their effect on protein activity is lacking. We used a high-throughput functional assay, in which the mutated protein is expressed together with a fluorescently labeled reporter in a cell-based assay. Using this system, we systematically assessed the activity of different combinations of RET fusions or oncogenic point mutations with one of three different common solvent front mutations and compared them to the activity of the individual mutations. Our results show that when a solvent front mutation is expressed on a RET oncogenic point mutation background, the solvent front mutation consistently decreases the oncogenic protein activity. This is supported by our observation that the individual solvent front mutations expressed on a RET WT background show an activity that is lower than that of the RET WT protein. On a RET fusion background the effect of solvent front mutations is more variable, with some RET fusion-solvent front mutation combinations showing a decreased activity and some not affecting the activity of the fusion protein. Across all mutations and fusions tested, the G810R and G810C mutations had a larger effect on RET activity than that of the G810S mutation. We also compared the effect of drug treatment (pralsetinib and selpercatinib) on RET oncogenic activity in the presence of the different solvent front mutations and observed that on all mutational backgrounds tested, the solvent front mutations have an effect on the response dynamics to the drug, and that the extent of the effect depends on the type of solvent front mutation, with G810R and G810C decreasing sensitivity to drug treatment to a larger extent compared to G810S. Together, our findings provide a better understanding of the differential effects of solvent front mutations on RET activity under different oncogenic contexts. Citation Format: Shay Rotkopf, DIkla Haham, Lea Birnbaum, Zohar Barbash, Gabi Tarcic. Analysis of RET solvent front mutations shows an effect on protein activity in tumor cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 403.

Pralsetinib treatment for multiple RET fusions in lung adenocarcinoma: a case report

Despite recent advances in treatments and knowledge of biomarkers, patients with metastatic lung cancer have a 5-year survival rate of 5%. Rearranged during transfection (RET) fusions occur in 1% to 2% of lung cancer patients. Pralsetinib has been used to treat non-small cell lung cancer with a single RET fusion; however, there have been no reports regarding its use in patients with multiple RET fusions. Genetic mutations in tumor tissues were tested using Amplification Refractory Mutation System-PCR and next-generation sequencing (NGS). Pleural fluids obtained from a male patient with non-small cell lung cancer were also used to detect genetic aberrations by NGS. Pleural fluid-based NGS revealed three RET rearrangements: CCDC6-RET (C2:R12), RET-NRG3 (R11:N3), and CCDC6-RET (C1:R12). All three rearrangements were targeted by pralsetinib, a RET fusion inhibitor. Pralsetinib drastically improved the patient’s condition within 4 days, and a partial response was achieved 1 week after pralsetinib was administered. We report for the first time the important clinical observation of a patient with multiple RET fusions who was effectively treated with pralsetinib.

LIBRETTO-001 cohort 7: A single-arm, phase 2 study of neoadjuvant selpercatinib in patients with resectable stage IB-IIIA RET fusion-positive NSCLC.

TPS8594 Background: Despite definitive surgery and perioperative chemotherapy, many patients with locoregional non-small cell lung cancer (NSCLC) continue to experience recurrent disease and limited survival. Although targeted therapies are standard treatment for metastatic NSCLC with genomic alterations, their use in the early-stage setting is still being characterized. Initial studies examining targeted therapy in neoadjuvant setting for early-stage epidermal growth factor receptor positive NSCLC has shown promise. Selpercatinib is a highly selective, potent, and central nervous system active rearranged during transfection (RET) inhibitor with demonstrated robust and sustained antitumor activity and manageable toxicity in patients with RET fusion-positive advanced NSCLC. Cohort 7 of the Phase 2, open-label, single arm LIBRETTO-001 study evaluates efficacy and safety of neoadjuvant selpercatinib in patients with resectable stage IB-IIIA RET fusion-positive NSCLC (NCT03157128). Methods: Key eligibility criteria include age ≥18 years; histologically confirmed stage IB–IIIA NSCLC (AJCC, version 8); presence of RET fusion in tumor (by PCR or NGS) or blood (by NGS) (pre-treatment biopsy confirmed); resectable and operable tumor; measurable disease (RECIST 1.1); and ECOG performance status 0-1. Key exclusion criteria include presence of other known oncogenic drivers; and concurrent investigational anticancer therapy. Eligible patients will undergo full staging including radiographic tumor measurements using CT, PET, and brain MRI at baseline and after two 28-day cycles of neoadjuvant selpercatinib, followed by surgery. Dosing regimen is 160 mg twice daily. Resected tumor specimens will be sent to an Independent Pathology Review Committee (IPRC) for evaluation. Patients may then be treated with stage-appropriate adjuvant therapy/surveillance, based on the treating physician’s decision, followed by selpercatinib until disease recurrence, unacceptable toxicity, withdrawal, or death, for a maximum treatment duration of 3 years. The primary endpoint is to determine the rate of major pathologic response (MPR) by IPRC, defined as ≤ 10% residual viable tumor cells in the surgically resected specimen. Efficacy based on the MPR will be assessed using the Simon's 2-stage design. In Stage I, 9 patients will be enrolled; if ≤1 patient achieves an MPR, the study will be stopped. Otherwise, at least 10 additional patients will be enrolled, with a total of 19 patients undergoing surgery. The rate of pathologic complete response (pCR) by IPRC, disease-free survival, and overall survival will be assessed as secondary endpoints. pCR rate will be determined at the time of surgery, indicating no remaining viable tumor cells. Safety of peri-operative treatment will be assessed, including 30- and 90-day post-operative readmission and mortality rates. Clinical trial information: NCT03157128.

Pralsetinib: chemical and therapeutic development with FDA authorization for the management of RET fusion-positive non-small-cell lung cancers.

Pralsetinib (PRL) is a selective Rearranged during Transfection (RET) inhibitor, developed by Blueprint Medicines Corporation for the treatment of RET fusion non-small-cell lung cancer (NSCLC), papillary thyroid cancer (PTC), and medullary thyroid carcinoma (MTC). RET is a known proto-oncogene found in NSCLC, PTC, and MTC. PRL was recently granted accelerated USFDA approval with the brand name GAVRETO™ on 4 September 2020 to treat metastatic RET fusion-positive NSCLC and was updated on 1 December 2020 with the addition of advanced and metastatic RET-altered MTC and PTC in the USA. On 19 November 2021, the European Commission granted conditional marketing authorization to PRL for use as a single agent in adult patients with RET fusion-positive advanced NSCLC. They were not previously treated with an RET inhibitor. This review article summarizes the milestones in the development of PRL, chemistry, chemical (synthesis) research and development, characterization and identification of PRL-resistant RET mutants, the structural basis of resistance to PRL, mechanism of action, pharmacokinetics, pharmacodynamic, adverse effects, and regulatory status, including ongoing clinical trial of PRL and other potential drug candidates, leading to this first approval of PRL for the treatment of various solid tumors (RET fusion NSCLC, MTC, and PTC).

The genomic characteristics of RET fusion positive tumors in Chinese non-small cell lung cancer (NSCLC) patients

BackgroundApproximately 1–2% of non-small cell lung cancer (NSCLC) patients harbor RET (rearranged during transfection) fusions. The oncogenic RET fusions could lead to constitutive kinase activation and oncogenesis.Methods1746 Chinese NSCLC patients were analyzed in this study. Tumor tissues were collected, and were formalin fixed, paraffin-embedded (FFPE) and archived. Peripheral blood (PB) samples were also collected from each patient as control. In addition, we selected 17 of them for cfDNA NGS testing and 14 tumor samples for immunohistochemistry testing using PD-L1 rabbit monoclonal antibody, clones 28-8 (Abcam, Cambridge, UK).ResultsOf the 1746 NSCLC cases, RET rearrangements were identified in 25 cases (1.43%) with locally advanced or metastatic NSCLC, of which 20 (80%) were female. We found that 14 out of 25 patients had an KIF5B-RET fusion, with KIF5B exon15-RET exon12, KIF5B exon23-RET exon12, and KIF5B exon24-RET exon11 detected in 14, 3, and 1 patients, respectively. We also identified one novel RET fusion partner PLCE1 and 4 intergenic-breakpoint fusions.ConclusionIn this study, using the hybrid capture based next generation sequencing (NGS) techniques, we revealed the genomic profiling for the patients with RET fusion-positive NSCLC. To the best of our knowledge, this is the first study that exhibited the detailed breakpoints of Chinese NSCLC patients with RET rearrangement, and we found a novel new partner PLCE1. The results provided genomic information for patients with RET fusion which is significant for personalized clinical management in the era of precision medicine.

Precision medicine in aggressive thyroid cancer: Moving beyond multitargeted tyrosine kinase inhibitors

Precision medicine in aggressive thyroid cancer: Moving beyond multitargeted tyrosine kinase inhibitors

Abstract 1221: The landscape of 2,706 RET alterations from 89,754 adult patients with cancer: Clinical implications

Abstract Background: Activating receptor-tyrosine kinase rearranged during transfection (RET) mutations and fusions have been recognized as potent drivers of oncogenesis in multiple malignancies. Recently, highly potent and selective RET inhibitors, selpercatinib and pralsetinib have been FDA approved for RET fusion+ NSCLC and selpercatinib for RET+ thyroid cancers. Here we present a comprehensive analysis of RET alterations in pan-cancer adult malignancies. Patients and methods: 96,324 samples from 89,754 patients available from AACR Project Genie database version 8 were analyzed for the prevalence of RET fusions, mutations, and copy number alterations in diverse cancer types accessed July 21, 2020. The races of the samples within the cohort were 69,962 (72.6%) white, 5,388 (5.6%) Black, 4,909 (5.1%) Asian, 163 (0.17%) Native American, 48 (0.05%) Pacific Islander, and 15,854 (16.5%) were unknown. Results: There were 56,382 (58.5%) samples from primary tumors, 24,204 (25.1%) samples from unspecified metastasis sites, 4,798 (5.0%) from distant organ metastasis, 1,379 (1.4%) from lymph node metastasis, 1,279 (1.3%) from local recurrence, and 8,282 (8.6%) unknown. In 96,324 tumor samples there were 2,706 (2.81%) RET alterations. This included 223 (0.23%) fusions, 1,689 RET mutations found (1.75%) in 21 tumor histologies, and 794 (0.82%) RET amplifications identified; where the most abundant tissues harboring RET fusions were NSCLC (n = 121), papillary thyroid cancer (n = 53), breast cancer (n = 8) and colorectal cancer (n = 7) and the most abundant tissues harboring RET missense mutations were NSCLC (n = 355), colorectal cancer (n = 292), melanoma (n = 236), and thyroid cancer (n = 127). NSCLC samples with RET fusions had significantly co-altered KRAS, SETD2, PVRL4, EZH1, and RRAGC. Conclusions: RET fusions represent extremely rate events in multiple cancers. RET missense mutations occur in 2% of malignancies. Most RET missense variants are described as variants of unknown significance, limiting the impact of precision oncology for the majority of patients with RET alterations. Further functional characterization of RET variants is warranted because RET is highly targetable with therapeutics. Citation Format: Jacob J. Adashek, Alexander Andreev-Drakhlin, Jason Roszik, Aakash P. Desai, Vivek Subbiah. The landscape of 2,706 RET alterations from 89,754 adult patients with cancer: Clinical implications [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 1221.