Genomic Heterogeneity Underlies Mixed Response to Tropomyosin Receptor Kinase Inhibition in Recurrent Glioma

Prevalence of NTRK Fusions in Canadian Solid Tumour Cancer Patients

INTRODUCTION

Neurotrophic tyrosine receptor kinase (NTRK) gene fusions occur in ~ 0.3% of all solid tumours but are enriched in some rare tumour types. Tropomyosin receptor kinase (TRK) inhibitors larotrectinib and entrectinib are approved as tumour-agnostic therapies for solid tumours harbouring NTRK fusions.

METHODS

This study investigated the prevalence of NTRK fusions in Canadian patients and also aimed to help guide NTRK testing paradigms through analysis of data reported from a national clinical diagnostic testing program between September 2019 and July 2021.

RESULTS

Of 1,687 patients included in the final analysis, NTRK fusions were detected in 0.71% (n = 12) of patients representing salivary gland carcinoma (n = 3), soft tissue sarcoma (n = 3), CNS (n = 3), and one in each of melanoma, lung, and colorectal cancer. All three salivary gland carcinomas contained ETV6-NTRK3 fusions. Thirteen (0.77%) clinically actionable incidental findings were also detected. Two of the 13 samples containing incidental findings were NTRK fusion-positive (GFOD1-NTRK2, FGFR3-TACC3 in a glioblastoma and AFAP1-NTRK2, BRAF c.1799T>A in a glioma). The testing algorithm screened most patient samples via pan-TRK immunohistochemistry (IHC), whereas samples from the central nervous system (CNS), pathognomonic cancers, and confirmed/ putative NTRK fusion-positive samples identified under research protocols were reflexed straight to next-generation sequencing (NGS).

CONCLUSION

These findings highlight the benefit and practicality of a diagnostic testing program to identify patients suitable for tumour-agnostic TRK inhibitor therapies, as well as other targeted therapies, due to clinically actionable incidental findings identified. Collectively, these findings may inform future guidance on selecting the appropriate testing approach per tumour type and on optimal NTRK testing algorithms.

Molecular and clinicopathologic features of gliomas harboring NTRK fusions

Fusions involving neurotrophic tyrosine receptor kinase (NTRK) genes are detected in ≤2% of gliomas and can promote gliomagenesis. The remarkable therapeutic efficacy of TRK inhibitors, which are among the first Food and Drug Administration-approved targeted therapies for NTRK-fused gliomas, has generated significant clinical interest in characterizing these tumors. In this multi-institutional retrospective study of 42 gliomas with NTRK fusions, next generation DNA sequencing (n = 41), next generation RNA sequencing (n = 1), RNA-sequencing fusion panel (n = 16), methylation profile analysis (n = 18), and histologic evaluation (n = 42) were performed. All infantile NTRK-fused gliomas (n = 7) had high-grade histology and, with one exception, no other significant genetic alterations. Pediatric NTRK-fused gliomas (n = 13) typically involved NTRK2, ranged from low- to high-histologic grade, and demonstrated histologic overlap with desmoplastic infantile ganglioglioma, pilocytic astrocytoma, ganglioglioma, and glioblastoma, among other entities, but they rarely matched with high confidence to known methylation class families or with each other; alterations involving ATRX, PTEN, and CDKN2A/2B were present in a subset of cases. Adult NTRK-fused gliomas (n = 22) typically involved NTRK1 and had predominantly high-grade histology; genetic alterations involving IDH1, ATRX, TP53, PTEN, TERT promoter, RB1, CDKN2A/2B, NF1, and polysomy 7 were common. Unsupervised principal component analysis of methylation profiles demonstrated no obvious grouping by histologic grade, NTRK gene involved, or age group. KEGG pathway analysis detected methylation differences in genes involved in PI3K/AKT, MAPK, and other pathways. In summary, the study highlights the clinical, histologic, and molecular heterogeneity of NTRK-fused gliomas, particularly when stratified by age group.