A Multi-institutional Effort With a Three-pronged Centralized Molecular Analysis to Optimize Detection of NTRK1,2,3 Fusions in Thyroid Cancer

Thyroid cancer is the most common neoplasm of the endocrine system. Most thyroid carcinomas originate from the follicular epithelium and are distinguished in differentiated forms (DTC): papillary (PTC) and follicular (FTC) carcinomas. Both have a favorable prognosis and account for approximately 80% and 10% of all thyroid neoplasms, respectively. The undifferentiated form represented by the anaplastic thyroid carcinoma (ATC) is less frequent (about 2%) and represents one of the most aggressive human tumors with a survival that rarely exceeds 6-12 months. Medullary thyroid carcinoma (MTC), deriving from parafollicular C cells, is relatively rare (approximately 5%) and is associated with an intermediate prognosis between differentiated and poorly differentiated forms.

As to the prevalence of NTRK lesions, many authoritative papers and reviews claim very high (up to 75%) NTRK fusion frequencies, particularly in the common PTC. However, an extensive PubMed analysis back to year 1990 does not provide convincing support for this claim.Several techniques for NTRK fusion diagnosis exist, including pan-Trk IHC, FISH, reverse transcription PCR, DNA-based next-generation sequencing (NGS), and RNA-based NGS. Each of these assays has unique features, advantages, and limitations, and familiarity with these assays is critical to appropriately screen for NTRK fusions.

The aim of this study is to determine the frequency of NTRK fusions in advanced thyroid cancer patients and to compare the diagnostic tecniques available (IHC, real-time PCR and NGS).