Case Report: Identification of a novel fusion co-existing with fusion in papillary thyroid carcinoma.

fusions are validated oncogenic drivers of various adult and pediatric tumor types, including thyroid cancer, and serve as a therapeutic target. Recently, tropomyosin receptor kinase (TRK) inhibitors, such as entrectinib and larotrectinib, display promising therapeutic efficacy in -positive solid tumors. Although some fusion partners have been identified in thyroid cancer, the spectrum of fusion is not fully characterized. In this study, a dual fusion was identified by targeted RNA-Seq in a 47-year-old female patient with papillary thyroid carcinoma. The patient harbors a novel in-frame fusion between exon 13 and exon 2, co-existing with a known in-frame fusion between exon 4 and exon 14. The dual fusion was validated by Sanger sequencing and fluorescence hybridization (FISH) but lack TRK protein expression as defined by pan-TRK immunohistochemistry (IHC). We supposed the pan-TRK IHC result to be falsely negative. In conclusion, we present the first case of a novel fusion co-existing with a known fusion in thyroid cancer. These findings extend the spectrum of translocation partners in fusion, and the effect of dual fusion on TRK inhibitor therapy and prognosis needs long-term follow-up.