Case report for an adolescent with germline RET mutation and alveolar rhabdomyosarcoma

Abstract

In this case report we evaluate the genetics of and scientific basis of therapeutic options for a 14-yr-old male patient diagnosed with metastatic PAX3–FOXO1 fusion positive alveolar rhabdomyosarcoma. A distinguishing genetic feature of this patient was a germline RET C634F mutation, which is a known driver of multiple endocrine neoplasia type 2A (MEN2A) cancer. Through sequential DNA and RNA sequencing analyses over the patient's clinical course, a set of gene mutations, amplifications, and overexpressed genes were identified and biological hypotheses generated to explore the biology of RET and coexisting signaling pathways in rhabdomyosarcoma. Somatic genetic abnormalities identified include CDK4 amplification and FGFR4 G388R polymorphism. Because of the initial lack of patient-derived primary cell cultures, these hypotheses were evaluated using several approaches including western blot analysis and pharmacological evaluation with molecularly similar alveolar rhabdomyosarcoma cell lines. Once a primary cell culture became available, the RET inhibitor cabozantinib was tested but showed no appreciable efficacy in vitro, affirming with the western blot negative for RET protein expression that RET germline mutation could be only incidental. In parallel, the patient was treated with cabozantinib without definitive clinical benefit. Parallel chemical screens identified PI3K and HSP90 as potential tumor-specific biological features. Inhibitors of PI3K and HSP90 were further validated in drug combination synergy experiments and shown to be synergistic in the patient-derived culture. We also evaluated the use of JAK/STAT pathway inhibitors in the context of rhabdomyosarcomas bearing the FGFR4 G388R coding variant. Although the patient succumbed to his disease, study of the patient's tumor has generated insights into the biology of RET and other targets in rhabdomyosarcoma.

Functional impact of a germline RET mutation in alveolar rhabdomyosarcoma

“…The research presented here complements our case report of a teenage male patient (denoted CF-00034) with a germline RET C634F mutation diagnosed with aRMS bearing the canonical PAX3:FOXO1 genomic rearrangement ( Crawford et al 2020 ). RET mutations occur in 1.8% of tumors across disparate disease types ( Kato et al 2017 ), and the PAX3:FOXO1 fusion occurs in 55% of ARMS cases ( Marshall and Grosveld 2012 ).…”

“…The clinical RET inhibitor cabozantinib was selected as the experimental RET inhibitor because of off-label clinical use in the previous case report ( Crawford et al 2020 ). Cabozantinib has been investigated clinically for RET-rearranged non-small-cell lung cancer ( Drilon et al 2016 ) and has shown significant clinical efficacy in RET M918T mutant medullary thyroid cancer ( Krajewska et al 2016 ).…”

“…Cabozantinib has been investigated clinically for RET-rearranged non-small-cell lung cancer ( Drilon et al 2016 ) and has shown significant clinical efficacy in RET M918T mutant medullary thyroid cancer ( Krajewska et al 2016 ). For combination therapies, we selected two clinical chemotherapy agents (vincristine and cyclophosphamide [tested as the prodrug mafosfamide]) not used to treat the index case patient described in the preceding manuscript ( Crawford et al 2020 ) and two clinical targeted inhibitor compounds (HDAC inhibitor entinostat [recently in a Phase I pediatric clinical trial, ADVL1513 /NCT02780804] and mTOR inhibitor temsirolimus). Each agent was first tested as a monotherapy to determine overall single agent efficacy across RET C634F transfected and null plasmid cell models ( Fig.…”

“…Given the association of mutant RET to cancer oncogenesis and metastasis, and previous reports of mutant RET in aRMS patients ( Agarwal et al 1997 ; Jones et al 2010 ; Crawford et al 2020 ), we investigated if the germline RET mutation coincident in a subset of aRMS patients may have contributed to the clinical course of CF-00034, and if the RET C634F mutation subsequently induces atypical susceptibilities in RMS tumor cells for patients with elevated RET expression or germline RET mutations.…”

A systematic review of the prevalence of pathogenic or likely pathogenic germline variants in individuals with FOXO1 fusion‐positive rhabdomyosarcoma

“…We included three case reports, four case series presenting RMS within specific CPS settings, and 12 large-scale germline sequencing studies in children/adolescent/young adult cancers that contained patients with RMS (Table 2). 10,12,14,23,28,[32][33][34][35][36][37][38][39][40][41][42][43][44][45] Selected studies were conducted in North America (n = 13), Europe (n = 4), Australia (n = 1), and Japan (n = 1).…”