TG-IGF1R: A Novel Receptor Tyrosine Kinase Fusion Oncogene in Pediatric Thyroid Cancer.

Background: Receptor tyrosine kinase (RTK) fusions of RET, NTRK1/3, and ALK are enriched among pediatric thyroid cancer patients with metastatic and persistent disease, and their oncoproteins represent attractive drug targets. Methods: We performed RNA-sequencing in a papillary thyroid cancer (PTC) lacking other frequent driver alterations. Results: We report a novel RTK fusion, TG-insulin-like growth factor 1 receptor gene (IGF1R), in a 17-year-old female patient with angioinvasive follicular variant PTC. The in-frame fusion protein preserves the cholinesterase-like domain of TG with dimerization properties and the transmembrane and kinase domain of IGF1R. The tumor sample shows increased IGF1R mRNA expression and tyrosine kinase phosphorylation, augmentation of Mitogen activated protein kinase (MAPK) transcriptional output genes, and decreased NIS levels. Conclusions: We reveal a novel targetable kinase fusion oncogene in thyroid cancer which is not incorporated in different thyroid-specific sequencing panels. The integration of IGF1R fusion screening in the next versions of thyroid-specific targeted next-generation sequencing panels may be beneficial to thyroid cancer patients.