Next-generation sequencing on fine needle aspirates in neck recurrence of thyroid cancers

Objective: Tumor molecular genotyping plays a key role in improving the management of advanced thyroid cancers. Molecular tests are classically performed on formalin-fixed, paraffin-embedded (FFPE) carcinoma tissue. However alternative molecular testing strategies are needed when FFPE tumoral tissue is unavailable. The objective of our study was to retrospectively assess the performance of targeted DNA and RNA-based next-generation sequencing (NGS) on the fine needle aspirate from thyroid cancer cervical recurrences to determine if this strategy is efficient in clinical practice. Design/Methods: A retrospective study of 33 patients who had had DNA and/or RNA-based NGS on ultrasound (US)-guided fine needle aspirates of cervical thyroid cancer recurrences in our Department from July 2019 to September 2022. Results: In total, 34 DNA and 32 RNA-based NGS analyses were performed. Out of the 34 DNA-based NGS performed, 27 (79%) were conclusive allowing the identification of an oncogenic driver for 18 patients (53%). The most common mutation (n = 13) was BRAF c.1799T>A. Out of the 32 RNA-based NGS performed, 26 were interpretable (81%) and no gene fusion was found. The identification of a BRAFV600E mutation was decisive for one patient in our series, who was prescribed dabrafenib and trametinib. Conclusion: NGS performed on fine needle aspirates of neck lymph node metastases enabled the identification of an oncogenic driver alteration in 53% of the cases in our series of advanced thyroid cancer patients and could significantly alter patient management. Significance statement This paper shows that thyroid cancer genotyping on the fine needle aspirate (FNA) of a metastatic neck lymph node recurrence can be performed efficiently. This strategy of genotyping appears particularly effective and safe when FFPE tissue is unavailable and when the spread of the disease requires systemic treatment. To the best of our knowledge, our data regarding DNA and RNA next generation sequencing on FNA of metastatic neck recurrences are the first ever published.