The discovery of actionable kinase gene rearrangements has revolutionized the therapeutic
landscape of thyroid carcinomas. Unsolved challenges include histopathologic recognition
of targetable cases, correlation between genotypes and tumor behavior, and evolving
resistance mechanisms against kinase inhibitors (KI). We present 62 kinase fusion-positive
thyroid carcinomas (KFTC), including 57 papillary thyroid carcinomas (PTC), two poorly
differentiated thyroid carcinomas (PDTC), two undifferentiated thyroid carcinomas
(ATC), and one primary secretory carcinoma (SC), in 57 adults and 5 adolescents. Clinical
records, post-operative histology, and molecular profiles were reviewed. Histologically,
all KFTC showed multinodular growth with prominent intratumoral fibrosis. Lymphovascular
invasion (95%), extrathyroidal extension, gross and microscopic (63%), and cervical
lymph node metastasis (79%) were common. Several kinase fusions were identified: STRN-ALK,
EML4-ALK, AGK-BRAF, CUL1-BRAF, MKRN1-BRAF, SND1-BRAF, TTYH3-BRAF, EML4-MET, TFG-MET,
IRF2BP2-NTRK1, PPL-NTRK1, SQSTM1-NTRK1, TPR-NTRK1, TPM3-NTRK1, EML4-NTRK3, ETV6-NTRK3,
RBPMS-NTRK3, SQSTM1-NTRK3, CCDC6-RET, ERC1-RET, NCOA4-RET, RASAL2-RET, TRIM24-RET,
TRIM27-RET, and CCDC30-ROS1. Individual cases also showed copy number variants of
EGFR and nucleotide variants and indels in pTERT, TP53, PIK3R1, AKT2, TSC2, FBXW7,
JAK2, MEN1, VHL, IDH1, PTCH1, GNA11, GNAQ, SMARCA4 and CDH1. In addition to thyroidectomy
and radioactive iodine, 10 patients received multi-kinase and/or selective kinase
inhibitor therapy, with 6 durable, objective responses and 4 with progressive disease.
Among 47 cases with >6 months of follow-up (median [range]: 41 [6 to 480] months),
persistent/recurrent disease, distant metastasis and thyroid cancer-related death
occurred in 57%, 38% and 6%, respectively. In summary, KFTC encompass a spectrum of
molecularly diverse tumors with overlapping clinicopathologic features and a tendency
for clinical aggressiveness. Characteristic histology with multinodular growth and
prominent fibrosis, particularly when there is extensive lymphovascular spread, should
trigger molecular testing for gene rearrangements, either in a step-wise manner by
prevalence or using a combined panel. Our findings further provide information on
molecularly therapy in radioiodine-refractory thyroid carcinoma.