Mechanisms of resistance to selective RET tyrosine kinase inhibitors in RET fusion-positive non-small-cell lung cancer.

Background: Rearranged during transfection (RET) gene fusions are a validated target in non-small-cell lung cancer (NSCLC). RET-selective inhibitors selpercatinib (LOXO-292) and pralsetinib (BLU-667) recently demonstrated favorable antitumor activity and safety profiles in advanced RET fusion-positive NSCLC, and both have received approval by the US Food and Drug Administration for this indication. Insights into mechanisms of resistance to selective RET inhibitors remain limited.
Patients and Methods: This study was performed at five institutions. Tissue and/or cell-free DNA was obtained from patients with RET fusion-positive NSCLC after treatment with selpercatinib or pralsetinib and assessed by next-generation sequencing (NGS) or MET FISH.
Results: We analyzed a total of 23 post-treatment tissue and/or plasma biopsies from 18 RET fusion-positive patients who received an RET-selective inhibitor (selpercatinib, n = 10; pralsetinib, n = 7; pralsetinib followed by selpercatinib, n = 1, with biopsy after each inhibitor). Three cases had paired tissue and plasma samples, of which one also had two serial resistant tissue specimens. The median progression-free survival on RET inhibitors was 6.3 months [95% confidence interval 3.6-10.8 months]. Acquired RET mutations were identified in two cases (10%), both affecting the RET G810 residue in the kinase solvent front. Three resistant cases (15%) harbored acquired MET amplification without concurrent RET resistance mutations, and one specimen had acquired KRAS amplification. No other canonical driver alterations were identified by NGS. Among 16 resistant tumor specimens, none had evidence of squamous or small-cell histologic transformation.
Conclusions: RET solvent front mutations are a recurrent mechanism of RET inhibitor resistance, although they occurred at a relatively low frequency. The majority of resistance to selective RET inhibition may be driven by RET-independent resistance such as acquired MET or KRAS amplification. Next-generation RET inhibitors with potency against RET resistance mutations and combination strategies are needed to effectively overcome resistance in these patients.
Competing Interests: Disclosure JJL has served as a compensated consultant or received honorarium from Chugai Pharma, Boehringer-Ingelheim, Pfizer, C4 Therapeutics, Nuvalent, Turning Point Therapeutics, Blueprint Medicines, and Genentech; received institutional research funds from Hengrui Therapeutics, Turning Point Therapeutics, Neon Therapeutics, Relay Therapeutics, Roche/Genentech, Pfizer, and Novartis; received CME funding from OncLive, MedStar Health, and Northwell Health; and received travel support from Pfizer. SVL served as a compensated consultant or on the advisory board for AstraZeneca, Blueprint, Boehringer-Ingelheim, Bristol-Myers Squibb, Celgene, G1 Therapeutics, Genentech/Roche, Guardant Health, Inivata, Janssen, Jazz, Lilly, Merck/MSD, PharmaMar, Pfizer, Regeneron, and Takeda; and received institutional research funding from Alkermes, AstraZeneca, Blueprint, Bristol-Myers Squibb, Corvus, Genentech, Lilly, Merck, Pfizer, Rain Therapeutics, RAPT, Spectrum, and Turning Point Therapeutics. CEM received honorarium from Novartis and Guardant Health; served on the advisory board for Genentech; and received research funding from Novartis and Revolution Medicines. ACT has served as a compensated consultant or received honorarium from Thermo Fisher. ID-J has received honoraria from Foundation Medicine; consulting fees from Boehringer Ingelheim and AstraZeneca; research support from Array, Genentech, Novartis, Pfizer, and Guardant Health; and travel support from Array and Pfizer. LJW has received personal fees from Bayer, Blueprint Medicines, Cue Biopharma, Exelixis, Genentech, and Rakuten Medical; received personal fees and nonfinancial support from Eisai, Lilly, Loxo Oncology, and Merck; and received institutional research funding from Loxo Oncology. ANH has received research support from Amgen, Pfizer, Novartis, Blueprint Medicines, Eli Lilly, Roche/Genentech, and Relay Therapeutics. MM-K has served as a compensated consultant for H3 Biomedicine and AstraZeneca; received institutional research support from Novartis. S-HIO has received personal fees from Pfizer, Merck, Takeda, AstraZeneca, Roche/Genentech, Daiichi Sankyo, Blueprint Medicines, and Janssen JNJ; and has stock ownership in Turning Point Therapeutics. DS-WT has served as a compensated consultant or received honorarium from Amgen, Boehringer-Ingelheim, Pfizer, C4 Therapeutics, Takeda, Bristol-Myers Squibb, MSD, Bayer, and Novartis; received institutional research funds from AstraZeneca, Pfizer, and Amgen; and received travel support from Pfizer and MSD. JFG has served as a compensated consultant or received honoraria from Bristol-Myers Squibb, Genentech, Ariad/Takeda, Loxo/Lilly, Blueprint, Oncorus, Regeneron, Gilead, AstraZeneca, Pfizer, Incyte, Novartis, Merck, Agios, Amgen, and Array; research support from Novartis, Genentech/Roche, and Ariad/Takeda; institutional research support from Bristol-Myers Squibb, Tesaro, Moderna, Blueprint, Jounce, Array Biopharma, Merck, Adaptimmune, Novartis, and Alexo; and has an immediate family member who is an employee of Ironwood Pharmaceuticals. All remaining authors have declared no conflicts of interest.
(Copyright © 2020 The Author(s). Published by Elsevier Ltd.. All rights reserved.)