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.

Expanded Access Program Pralsetinib in Advanced Non-Small Cell Lung Cancer with Rearranged during Transfection (RET) Gene Rearrangement

PURPOSE

Rearranged during transfection (RET) gene rearrangement is a well-known driver event in non-small cell lung cancer (NSCLC). Pralsetinib is a selective inhibitor of RET kinase and has shown efficacy in oncogenic RET-altered tumors. This study evaluated the efficacy and safety of expanded access program (EAP) use of pralsetinib in pretreated, advanced NSCLC patients with RET rearrangement.

MATERIALS AND METHODS

Patients who received pralsetinib as part of the EAP at Samsung Medical Center were evaluated through a retrospective chart review. The primary endpoint was overall response rate (ORR) per the Response Evaluation Criteria in Solid Tumors (RECIST) ver. 1.1 guidelines. Secondary endpoints were duration of response, progression-free survival (PFS), overall survival (OS), and safety profiles.

RESULTS

Between April 2020 and September 2021, 23 of 27 patients were enrolled in the EAP study. Two patients who were not analyzed due to brain metastasis and two patients whose expected survival was within 1 month were excluded from the analysis. After a median follow-up period of 15.6 months (95% confidence interval [CI], 10.0 to 21.2), ORR was 56.5%, the median PFS was 12.1 months (95% CI, 3.3 to 20.9), and the 12-month OS rate was 69.6%. The most frequent treatment-related adverse events (TRAEs) were edema (43.5%) and pneumonitis (39.1%). A total of 8.7% of patients experienced extra-pulmonary tuberculosis. TRAEs with a common grade of three or worse were neutropenia (43.5%) and anemia (34.8%). Dose reduction was required in nine patients (39.1%).

CONCLUSION

Pralsetinib presents a clinical benefit when used in patients with RET-rearranged NSCLC, consistent with a pivotal study.

TMEM127 suppresses tumor development by promoting RET ubiquitination, positioning, and degradation

The TMEM127 gene encodes a transmembrane protein of poorly known function that is mutated in pheochromocytomas, neural crest-derived tumors of adrenomedullary cells. Here, we report that, at single-nucleus resolution, TMEM127-mutant tumors share precursor cells and transcription regulatory elements with pheochromocytomas carrying mutations of the tyrosine kinase receptor RET. Additionally, TMEM127-mutant pheochromocytomas, human cells, and mouse knockout models of TMEM127 accumulate RET and increase its signaling. TMEM127 contributes to RET cellular positioning, trafficking, and lysosome-mediated degradation. Mechanistically, TMEM127 binds to RET and recruits the NEDD4 E3 ubiquitin ligase for RET ubiquitination and degradation via TMEM127 C-terminal PxxY motifs. Lastly, increased cell proliferation and tumor burden after TMEM127 loss can be reversed by selective RET inhibitors in vitro and in vivo. Our results define TMEM127 as a component of the ubiquitin system and identify aberrant RET stabilization as a likely mechanism through which TMEM127 loss-of-function mutations cause pheochromocytoma.

FDA Approval Summary: Selpercatinib for the Treatment of Advanced RET Fusion-Positive Solid Tumors

On September 21, 2022, the FDA granted accelerated approval to selpercatinib (Retevmo, Eli Lilly and Company) for the treatment of adult patients with locally advanced or metastatic solid tumors with a rearranged during transfection (RET) gene fusion that have progressed on or following prior systemic treatment or who have no satisfactory alternative treatment options. The approval was based on data from Study LOXO-RET-17001 (LIBRETTO-001; NCT03157128), an international, non-randomized, multi-cohort clinical trial that included patients with advanced solid tumors harboring RET alterations. The overall response rate in 41 patients with locally advanced or metastatic RET fusion-positive solid tumors other than non-small cell lung cancer (NSCLC) or thyroid cancer was 44% [95% confidence interval (CI), 28%-60%], with median duration of response 24.5 months (95% CI, 9.2-not evaluable). Patients with 10 of 14 tumor types with a variety of fusion partners had objective responses, including patients with the following tumors: pancreatic adenocarcinoma, colorectal, salivary, unknown primary, breast, soft-tissue sarcoma, bronchial carcinoid, ovarian, small intestine, and cholangiocarcinoma. The recommendation for approval was supported by results from LIBRETTO-001 in patients with RET fusion-positive NSCLC and thyroid cancer, which formed the basis of prior approvals in these tumor types. The most common adverse reactions (>25%) were edema, diarrhea, fatigue, dry mouth, hypertension, abdominal pain, constipation, rash, nausea, and headache. This is the first tissue-agnostic approval of a RET-directed targeted therapy.

Medullary Thyroid Cancer: Updates and Challenges

A personalized approach to the management of medullary thyroid cancer (MTC) presents several challenges; however, in the past decade significant progress has been made in both diagnostic and treatment modalities. Germline rearranged in transfection (RET) testing in multiple endocrine neoplasia 2 and 3, and somatic RET testing in sporadic MTC have revolutionized the treatment options available to patients. Positron emission tomography imaging with novel radioligands has improved characterization of disease and a new international grading system can predict prognosis. Systemic therapy for persistent and metastatic disease has evolved significantly with targeted kinase therapy especially for those harboring germline or somatic RET variants. Selpercatinib and pralsetinib are highly selective RET kinase inhibitors that have shown improved progression-free survival with better tolerability than outcomes seen in earlier multikinase inhibitor studies. Here we discuss changes in paradigms for MTC patients: from determining RET alteration status upfront to novel techniques for the evaluation of this heterogenous disease. Successes and challenges with kinase inhibitor use will illustrate how managing this rare malignancy continues to evolve.

ALK, ROS1, RET and NTRK1-3 Gene Fusions in Colorectal and Non-Colorectal Microsatellite-Unstable Cancers

This study aimed to conduct a comprehensive analysis of actionable gene rearrangements in tumors with microsatellite instability (MSI). The detection of translocations involved tests for 5'/3'-end expression imbalance, variant-specific PCR and RNA-based next generation sequencing (NGS). Gene fusions were detected in 58/471 (12.3%) colorectal carcinomas (CRCs), 4/69 (5.8%) gastric cancers (GCs) and 3/65 (4.6%) endometrial cancers (ECs) (ALK: 8; RET: 12; NTRK1: 24; NTRK2: 2; NTRK3: 19), while none of these alterations were observed in five cervical carcinomas (CCs), four pancreatic cancers (PanCs), three cholangiocarcinomas (ChCs) and two ovarian cancers (OCs). The highest frequency of gene rearrangements was seen in KRAS/NRAS/BRAF wild-type colorectal carcinomas (53/204 (26%)). Surprisingly, as many as 5/267 (1.9%) KRAS/NRAS/BRAF-mutated CRCs also carried tyrosine kinase fusions. Droplet digital PCR (ddPCR) analysis of the fraction of KRAS/NRAS/BRAF mutated gene copies in kinase-rearranged tumors indicated that there was simultaneous co-occurrence of two activating events in cancer cells, but not genetic mosaicism. CRC patients aged above 50 years had a strikingly higher frequency of translocations as compared to younger subjects (56/365 (15.3%) vs. 2/106 (1.9%), p = 0.002), and this difference was particularly pronounced for tumors with normal KRAS/NRAS/BRAF status (52/150 (34.7%) vs. 1/54 (1.9%), p = 0.001). There were no instances of MSI in 56 non-colorectal tumors carrying ALK, ROS1, RET or NTRK1 rearrangements. An analysis of tyrosine kinase gene translocations is particularly feasible in KRAS/NRAS/BRAF wild-type microsatellite-unstable CRCs, although other categories of tumors with MSI also demonstrate moderate occurrence of these events.

Efficacy and Safety of RET-Specific Kinase Inhibitors in RET-Altered Cancers: A Systematic Review

RET proto-oncogene encodes receptor tyrosine kinase. Selpercatinib and pralsetinib are the only RET-specific tyrosine kinase inhibitors approved by FDA in RET-altered tumors. We searched PubMed, Embase, Cochrane, WOS, and Clinicaltrials.gov. Objective-response, complete-response, and partial-response were 60-89%, 0-11%, and 55-89%, respectively, with the use of RET-specific drugs. ≥Grade 3 adverse events were seen in 28-53% of the patients, with hypertension, change in ALT, QT prolongation, neutropenia, and pneumonitis among the common side effects. Hence, selpercatinib and pralsetinib were effective and well tolerated by most of the patients with RET-altered tumors.

Amplification of Wild-Type RET Represents a Novel Molecular Subtype of Several Cancer Types With Clinical Response to Selpercatinib

PURPOSE

RET rearrangements and RET activating point mutations represent targetable genomic alterations in advanced solid tumors. However, the frequency and clinicopathologic characteristics of wild-type RET amplification in cancer and its potential role as a targetable oncogenic driver are not well-characterized.

METHODS

In two institutional cohorts of patients with solid cancers from the Dana-Farber Cancer Institute (DFCI) and Memorial Sloan Kettering Cancer Center (MSKCC) whose tumors underwent next-generation sequencing (NGS), the frequency and clinicopathologic features of wild-type RET amplification in the absence of RET rearrangements or activating mutations was assessed. The findings were validated using merged data from The Cancer Genome Atlas (TCGA), Genomics Evidence Neoplasia Information Exchange (GENIE), and China Pan-Cancer data sets.

RESULTS

The frequency of wild-type RET amplification across all solid cancers was 0.08% (26 of 32,505) in the DFCI cohort, 0.05% (26 of 53,152) in the MSKCC cohort, and 0.25% (71 of 28,623) in the cohort from TCGA, GENIE, and China Pan-Cancer. Cancer types with RET amplification included non-small-cell lung cancer (NSCLC), hepatobiliary cancer, prostate cancer, breast cancer, and others. The median RET copy number in RET-amplified cases was 7.5 (range, 6-36) in the DFCI cohort and 5.7 (range, 4-27.7) in the MSKCC cohort. Among 11 RET-amplified NSCLCs, eight had no other concurrent driver mutations. Finally, we report on a 69-year-old man with recurrent NSCLC harboring high-level wild-type RET amplification (22-28 copies) as the only identified putative genomic driver who experienced both a systemic and intracranial confirmed response to the RET inhibitor selpercatinib.

CONCLUSION

Amplification of wild-type RET represents a novel, targetable molecular subset of cancer.

Expression of Glial Cell-Derived Neurotrophic Factor Receptors Within Nucleus Ambiguus During Rat Development

OBJECTIVE

The nucleus ambiguus (NAmb) is a column of neurons in the medulla oblongata, involved in bulbar functions. Expression of Glial Cell-Derived Neurotrophic Factor (GDNF) and its receptors (GDNFR) is observed within the cell bodies during reinnervation following recurrent laryngeal nerve (RLN) injury. Little is known regarding GDNFR expression in the formation of the NAmb and the laryngeal innervation during embryogenesis. Understanding the timing and pattern of GDNFR expression in embryogenesis versus after RLN injury may provide insights into therapeutic targets for regeneration after RLN injury.

STUDY DESIGN

Laboratory experiment.

METHODS

Rat brainstems at E14.5/E16.5/E18.5/E20.5/adult were stained for GDNFR: GFRα-1/GFRα-2/GFRα-3/Ret. Islet1 and choline acetyltransferase were used as cell body markers. Sections were observed using fluorescent microscopy and quantified through manual cell counting.

RESULTS

Expression of GFRα-1, GFRα-3, and Ret was identified within the NAmb, hypoglossal, and facial nuclei of the adult medulla. During development, GFRα-1 immunoreactivity was seen at E20.5. GFRα-2 expression was not observed at any timepoint. GFRα-3 expression began at E16.5. Ret expression within nerve fibers in the NAmb were observed beginning at E14.5, but never in the cell bodies.

CONCLUSION

Embryonic GDNFR expression in the NAmb differs from that of the adult after RLN injury. The developing brainstem experienced upregulation at discrete timepoints with signaling sustained through adulthood. In contrast, adult RLN-transected rats experienced patterns of up and down regulation. GFRα-1 may contribute to muscle targeting and neuromuscular junction maturation, GFRα-3 may contribute to both, as well as axon guidance. It is likely that GDNF is functioning via a Ret-independent pathway.

LEVEL OF EVIDENCE

NA Laryngoscope, 133:2240-2247, 2023.

PLM-101 is a novel and potent FLT3/RET inhibitor with less adverse effects in the treatment of acute myeloid leukemia

Acute myeloid leukemia (AML) is a prevalent form of leukemia in adults. As its survival rate is low, there is an urgent need for new therapeutic options. In AML, FMS-like tyrosine kinase 3 (FLT3) mutations are common and have negative outcomes. However, current FLT3-targeting agents, Midostaurin and Gilteritinib, face two significant issues, specifically the emergence of acquired resistance and drug-related adverse events leading to treatment failure. Rearranged during transfection (RET), meanwhile, is a proto-oncogene linked to various types of cancer, but its role in AML has been limited. A previous study showed that activation of RET kinase enhances FLT3 protein stability, leading to the promotion of AML cell proliferation. However, no drugs are currently available that target both FLT3 and RET. This study introduces PLM-101, a new therapeutic option derived from the traditional Chinese medicine indigo naturalis with potent in vitro and in vivo anti-leukemic activities. PLM-101 potently inhibits FLT3 kinase and induces its autophagic degradation via RET inhibition, providing a superior mechanism to that of FLT3 single-targeting agents. Single- and repeated-dose toxicity tests conducted in the present study showed no significant drug-related adverse effects. This study is the first to present a new FLT3/RET dual-targeting inhibitor, PLM-101, that shows potent anti-leukemic activity and fewer adverse effects. PLM-101, therefore, should be considered for use as a potential therapeutic agent for AML.

Patterns of Treatment Failure After Selective Rearranged During Transfection (RET) Inhibitors in Patients With Metastatic Medullary Thyroid Carcinoma

PURPOSE

Medullary thyroid cancer (MTC) harbors frequent mutations in RET oncogene. Selective RET inhibitors (RETi) have emerged as effective treatments. However, resistance almost invariably occurs.

METHODS

MTC patients who were initiated on RETi between 2018 and 2022 were included. Baseline characteristics, RET mutational status, RETi response, available tumor tissue and molecular profiles sampled pre- and post-RETi were analyzed.

RESULTS

Among 46 MTC patients on RETi during the study period, 26 patients had discontinued at data cut-off because of progression (n = 16), death (n = 4), and toxicity (n = 6). The most frequent RET mutations at baseline were p.M918T (n = 29), and p.C634X (n = 6). Pre- and post-RETi molecular profiles were available in 14 patients. There was no primary resistance on pre-RETi samples. Post-RETi profiles revealed a bypass mechanism of resistance in 75% of the cases including RAS genes mutations (50%), FGFR2 and ALK fusions and and MYC p.P44L. RET solvent from and hinge region mutations was the only resistance mechanisms in 25% of the cases. Tumor samples from initial thyroidectomy, pre- and post-RETi, from six patients, showed an increase of the mean Ki 67-index of 7%, 17% and 40% respectively (P = 0.037) and a more aggressive poorly differentiated histology in three patients.

DISCUSSION

Bypass resistance may be the most frequent mechanism of progression under RETi. A more aggressive histology may arise following RETi and warrants further investigation.

Germline founder variant c.1998delinsTTCT in the RET oncogene: a cohort study in 15 Belgian families

OBJECTIVE

The c.1998delinsTTCT variant in the RET gene (codon 666) is linked to medullary thyroid carcinoma in Belgium. We aimed to study the clinical phenotype and the age-dependent penetrance in predictive variant carriers.

DESIGN

Retrospective study of index patients and predictive variant carriers, identified through familial cascade testing between 2001 and 2020.

RESULTS

The total cohort comprised 119 patients: 15 index patients, 102 heterozygous, and 2 homozygous predictive variant carriers. Among heterozygous carriers, high suspicion of clinical disease was present in 25 patients at initial evaluation and in 3 patients during follow-up. No high suspicion of clinical disease was observed during surveillance in 56 patients, and 18 patients did not proceed to screening for clinical disease. Compared to index patients, surgically treated heterozygous predictive variant carriers had a lower presurgical basal calcitonin, a lower disease stage, less need for adjuvant therapy, and higher chances of remission. In heterozygous carriers, median age at developing high suspicion of disease is 52 years (range 7-75), with a predicted penetrance of 62% (9% SE) at the age of 70 years. Two patients were identified with pheochromocytoma and 1 patient with primary hyperparathyroidism. The 2 homozygous predictive variant carriers presented with higher disease severity at first clinical evaluation.

CONCLUSION

The c.1998delinsTTCT variant in the RET gene is pathogenic and associated with a moderate risk for medullary thyroid carcinoma and rarely with other multiple endocrine neoplasia type 2A (MEN2A) manifestations. Active surveillance is a possible option in heterozygous gene carriers with a negative first clinical evaluation.

Detecting ALK, ROS1, and RET fusions and the METΔex14 splicing variant in liquid biopsies of non-small-cell lung cancer patients using RNA-based techniques

ALK, ROS1, and RET fusions and MET∆ex14 variant associate with response to targeted therapies in non-small-cell lung cancer (NSCLC). Technologies for fusion testing in tissue must be adapted to liquid biopsies, which are often the only material available. In this study, circulating-free RNA (cfRNA) and extracellular vesicle RNA (EV-RNA) were purified from liquid biopsies. Fusion and MET∆ex14 transcripts were analyzed by nCounter (Nanostring) and digital PCR (dPCR) using the QuantStudio® System (Applied Biosystems). We found that nCounter detected ALK, ROS1, RET, or MET∆ex14 aberrant transcripts in 28/40 cfRNA samples from positive patients and 0/16 of control individuals (70% sensitivity). Regarding dPCR, aberrant transcripts were detected in the cfRNA of 25/40 positive patients. Concordance between the two techniques was 58%. Inferior results were obtained when analyzing EV-RNA, where nCounter often failed due to a low amount of input RNA. Finally, results of dPCR testing in serial liquid biopsies of five patients correlated with response to targeted therapy. We conclude that nCounter can be used for multiplex detection of fusion and MET∆ex14 transcripts in liquid biopsies, showing a performance comparable with next-generation sequencing platforms. dPCR could be employed for disease follow-up in patients with a known alteration. cfRNA should be preferred over EV-RNA for these analyses.

Unleashing a Lazarus Effect With Selpercatinib in a Never-Smoker Patient With Stage IV, Chemo-Immunotherapy Refractory, RET C630Y-Mutant, Small-Cell Lung Cancer: A First Case Report

The discovery of a RET gene mutation opens the door to targeted therapy in SCLC. #LCSM

Maternal Vitamin A Status as a Risk Factor of Hirschsprung Disease in the Child

INTRODUCTION

The gene-environment interaction of the REarranged during Transfection ( RET ) gene with vitamin A in the etiopathogenesis of Hirschsprung disease (HSCR) has been suggested in rodents. The aim of this study was to evaluate vitamin A status in mothers of children with HSCR and to assess its association with pathogenic variants of the RET gene in affected children.

METHODS

This was a case-control study of stable isotope-based vitamin A measurement stores of mothers of children diagnosed with HSCR (within 8 months from birth, n = 7) and age-matched mothers of normal children (n = 6). Next-generation sequencing of RET exons, along with their upstream promoter region, was performed in the 7 HSCR proband-parent triads to evaluate pathogenic variants.

RESULTS

Maternal vitamin A stores in the HSCR group was almost 50% that of those in controls, tending toward significance (0.50 ± 0.17 vs 0.89 ± 0.51 μmol/g respectively, P = 0.079). Two novel pathogenic de novo mutations were identified in 2 cases, and a rare single-nucleotide deletion was detected in the 3.5-kb RET upstream region, in a heterozygous state, in all 7 proband-parent triads. Low-penetrance RET haplotypes associated with HSCR were detected in 5 cases.

DISCUSSION

Mothers with children with HSCR had lower vitamin A liver stores than mothers with normal children, and the children who were affected had HSCR despite having no established pathogenic RET variants. Lower maternal vitamin A status may increase the penetrance of genetic mutations in RET , and vitamin-A mediated gene-environment interactions may underpin some of the etiology of HSCR.

Ret deficiency decreases neural crest progenitor proliferation and restricts fate potential during enteric nervous system development

The receptor tyrosine kinase RET plays a critical role in the fate specification of enteric neural crest-derived cells (ENCDCs) during enteric nervous system (ENS) development. RET loss of function (LoF) is associated with Hirschsprung disease (HSCR), which is marked by aganglionosis of the gastrointestinal (GI) tract. Although the major phenotypic consequences and the underlying transcriptional changes from Ret LoF in the developing ENS have been described, cell type- and state-specific effects are unknown. We performed single-cell RNA sequencing on an enriched population of ENCDCs from the developing GI tract of Ret null heterozygous and homozygous mice at embryonic day (E)12.5 and E14.5. We demonstrate four significant findings: 1) Ret-expressing ENCDCs are a heterogeneous population comprising ENS progenitors as well as glial- and neuronal-committed cells; 2) neurons committed to a predominantly inhibitory motor neuron developmental trajectory are not produced under Ret LoF, leaving behind a mostly excitatory motor neuron developmental program; 3) expression patterns of HSCR-associated and Ret gene regulatory network genes are impacted by Ret LoF; and 4) Ret deficiency leads to precocious differentiation and reduction in the number of proliferating ENS precursors. Our results support a model in which Ret contributes to multiple distinct cellular phenotypes during development of the ENS, including the specification of inhibitory neuron subtypes, cell cycle dynamics of ENS progenitors, and the developmental timing of neuronal and glial commitment.

Osimertinib and Selpercatinib Efficacy, Safety, and Resistance in a Multicenter, Prospectively Treated Cohort of EGFR-Mutant and RET Fusion-Positive Lung Cancers

PURPOSE

Acquired RET fusions have been reported at resistance to treatment with EGFR inhibitors in EGFR-mutant non-small cell lung cancer (NSCLC); however, a multicenter cohort of patients with EGFR-mutant lung cancers treated with osimertinib and selpercatinib for RET fusion-mediated osimertinib resistance has not previously been published.

PATIENTS AND METHODS

Patients who received selpercatinib in combination with osimertinib on a prospective expanded access clinical trial (NCT03906331) and single-patient compassionate use programs across five countries were centrally analyzed. All patients had advanced EGFR-mutant NSCLC with a RET fusion detected from tissue or plasma following osimertinib therapy. Clinicopathologic and outcomes data were collected.

RESULTS

Fourteen patients with EGFR-mutant and RET fusion-positive lung cancers who experienced prior progression on osimertinib received osimertinib and selpercatinib. EGFR exon 19 deletions (±T790M, 86%) and non-KIF5B fusions (CCDC6-RET 50%, NCOA4-RET 36%) predominated. Osimertinib 80 mg daily and selpercatinib 80 mg twice daily were the most commonly administered dosages. The response rate, disease control rate, and median treatment duration were 50% [95% confidence interval (CI), 25%-75%, n = 12], 83% (95% CI, 55%-95%), and 7.9 months (range, 0.8-25+), respectively. Resistance was complex, involving EGFR on-target (EGFR C797S), RET on-target (RET G810S), and off-target (EML4-ALK/STRN-ALK, KRAS G12S, BRAF V600E) mechanisms; RET fusion loss; or polyclonal mechanisms.

CONCLUSIONS

For patients with EGFR-mutant NSCLC with an acquired RET fusion as a mechanism of EGFR inhibitor resistance, the addition of selpercatinib to osimertinib was feasible and safe and offered clinical benefit, supporting the prospective evaluation of this combination. See related commentary by Krebs and Popat, p. 2951.

D898_E901 RET Deletion Is Oncogenic, Responds to Selpercatinib, and Treatment Resistance Can Arise Via RET-Independent Mechanisms

PURPOSE

We analyzed the oncogenic potential of RET Δ898-901 mutant and its response to selpercatinib, vandetanib, and cabozantinib in vitro and in a clinical case.

MATERIALS AND METHODS

A 35-year-old man with a medullary thyroid cancer (MTC) harboring a somatic D898_E901 RET deletion was sequentially treated with vandetanib, selpercatinib, cabozantinib, and fluorouracil (5-FU)-dacarbazine. Functional study of RET Δ898-901 mutant was performed in HEK-293T, NIH-3T3, and Ba/F3 cells. RET C634R and wild-type cells served as positive and negative controls, respectively.

RESULTS

The patient showed primary resistance to vandetanib and secondary resistance to selpercatinib after 12 months. Comprehensive next-generation sequencing of a progressing lesion during selpercatinib showed no additional RET mutation but an acquired complete genetic loss of CDKN2A, CDKN2B, and MTAP genes. Subsequent treatment with cabozantinib and 5-FU-dacarbazine had poor efficacy. In vitro, RET Δ898-901 showed higher ligand-independent RET autophosphorylation compared with RET C634R and similar proliferation rates in cell models. Subcutaneous injection of Δ898-901 NIH 3T3 cells in nude mice produced tumors of around 500 mm3 in 2 weeks, similarly to RET C634R cells. Selpercatinib inhibited cell growth of Ba/F3 RET Δ898-901 and RET C634R with a similar half maximal inhibitory concentration (IC50) of approximately 3 nM. Vandetanib was five-fold less effective at inhibiting cell growth promoted by RET Δ898-901 mutant (IC50, 564 nM) compared with RET C634R one (IC50, 91 nM). Cabozantinib efficiently inhibited Ba/F3 RET C634 proliferation (IC50, 25.9 nM), but was scarcely active in Ba/F3 RET 898-901 (IC50 > 1,350 nM).

CONCLUSION

D898_E901 RET deletion is a gain-of-function mutation and responds to tyrosine kinase inhibitors in MTC. RET Δ898-901 mutant is sensitive to selpercatinib and vandetanib, and acquired resistance to selpercatinib may develop via RET-independent mechanisms.

A novel PIBF1-RET gene fusion identified from a stage IA lung adenocarcinoma: A case report

INTRODUCTION

Rearranged during transfection (RET) gene fusions occur in 0.7% to 2% in lung cancer and 1% to 2% in non-small cell lung cancer. Systemic therapies for RET fusion-positive non-small cell lung cancer consist mostly of targeted therapy with RET inhibitors such as selpercatinib and pralsetinib. To date, approximately 40 fusion partners have been reported. Herein, we report a novel progesterone immunomodulatory binding factor 1 (PIBF1)-RET gene fusion identified from a stage IA lung adenocarcinoma and was further validated by RNA sequencing analysis.

PATIENT CONCERNS

A 55-year-old male smoker was found by chest computed tomography to have a solid nodule in the right lower lobe of the lung and enlarged mediastinal lymph nodes.

DIAGNOSES

The patient was then diagnosed with stage IA lung adenocarcinoma (T1N0M0).

INTERVENTION

The patient then underwent thoracoscopic lobectomy of the right lower lobe and mediastinal lymph node dissection. Molecular testing with a targeted panel of 8 lung cancer-associated driver genes detected a novel PIBF1-RET (P16:R12) fusion, which putatively encodes a gene in which the first 16 exons of PIBF1 was concatenated to RET exon 13 and its downstream sequence, retaining the RET kinase domain. The genomic translocation was further validated by RNA sequencing with a panel of 115 cancer-associated genes, which found no other aberrations.

OUTCOMES

The patient was discharged 3 days after surgery.

CONCLUSION

We report a novel PIBF1-RET fusion in early-stage lung adenocarcinoma. This finding expands the spectrum of RET fusion partners and warrants further studies in characterizing the oncogenic role of this genomic aberration and response to RET-targeted therapies.

Two drugs for RET-altered cancers (Retevmo and Gavreto)

The oral kinase inhibitors selpercatinib (Retevmo – Lilly) and pralsetinib (Gavreto – Blueprint Medicines/Genentech) have been approved by the FDA for treatment of advanced or metastatic RET-mutant or RET fusion-positive cancers.

Selpercatinib for adult patients with locally advanced or metastatic RET-altered solid tumors

INTRODUCTION

The rearranged during transfection (RET) mutation is an oncogene driver for the development of cancer. Selpercatinib is a highly selective RET inhibitor that has demonstrated anti-tumor activity in RET-mutated cancers. Selpercatinib is approved for use in RET fusion-positive non-small-cell lung cancer (NSCLC), RET-mutated medullary thyroid cancer, RET fusion-positive thyroid cancer, and RET fusion-positive solid tumors.

AREAS COVERED

This review summarizes the pharmacology, efficacy, safety, and resistance mechanism of selpercatinib.

EXPERT OPINION

Selpercatinib has demonstrated durable responses with a favorable safety profile making it an excellent treatment option for RET-mutated cancers. Clinical trials are currently underway to determine the optimal sequencing of selpercatinib in RET fusion-positive lung and RET-mutated medullary thyroid cancer in the first-line setting compared to the current standard of care. Selpercatinib has shown promising anti-tumor activity in various RET-altered solid tumors opening a new treatment option for these patients.