Diagnostic Limitation of Fine-Needle Aspiration (FNA) on Indeterminate Thyroid Nodules Can Be Partially Overcome by Preoperative Molecular Analysis: Assessment of RET/PTC1 Rearrangement in BRAF and RAS Wild-Type Routine Air-Dried FNA Specimens

Abstract

Molecular markers are helpful diagnostic tools, particularly for cytologically indeterminate thyroid nodules. Preoperative <i>RET/PTC1</i> rearrangement analysis in <i>BRAF</i> and <i>RAS</i> wild-type indeterminate thyroid nodules would permit the formulation of an unambiguous surgical plan. Cycle threshold values according to the cell count for detection of the <i>RET/PTC1</i> rearrangement by real-time reverse transcription-polymerase chain reaction (RT-PCR) using fresh and routine air-dried TPC1 cells were evaluated. The correlation of <i>RET/PTC1</i> rearrangement between fine-needle aspiration (FNA) and paired formalin-fixed paraffin-embedded (FFPE) specimens was analyzed. <i>RET/PTC1</i> rearrangements of 76 resected <i>BRAF</i> and <i>RAS</i> wild-type classical PTCs were also analyzed. Results of RT-PCR and the Nanostring were compared. When 100 fresh and air-dried TPC1 cells were used, expression of <i>RET/PTC1</i> rearrangement was detectable after 35 and 33 PCR cycles, respectively. The results of <i>RET/PTC1</i> rearrangement in 10 FNA and paired FFPE papillary thyroid carcinoma (PTC) specimens showed complete correlation. Twenty-nine (38.2%) of 76 <i>BRAF</i> and <i>RAS</i> wild-type classical PTCs had <i>RET/PTC1</i> rearrangement. Comparison of <i>RET/PTC1</i> rearrangement analysis between RT-PCR and the Nanostring showed moderate agreement with a κ value of 0.56 (<i>p</i> = 0.002). The <i>RET/PTC1</i> rearrangement analysis by RT-PCR using routine air-dried FNA specimen was confirmed to be technically applicable. A significant proportion (38.2%) of the <i>BRAF</i> and <i>RAS</i> wild-type PTCs harbored <i>RET/PTC1</i> rearrangements.