Fine needle aspirate (FNA) cytology is the first-line gold standard for initial diagnosis of thyroid cancer. Surgical pathology of formalin fixed paraffin embedded (FFPE) resected tissues remains the ultimate standard. While FFPE tissues have been used retrospectively to develop specific molecular diagnostic biomarkers, the full investigative and clinical diagnostic potential of archived cytology/histopathology slides has not yet been fully realized.
We have previously developed and reported on the clinical utility of a combined approach incorporating NGS-based oncogene mutation detection (ThyGenX®) and broad panel microRNA (miR) benign/malignant classifier (ThyraMIR®) performed on thyroid nodule FNA fresh samples. ThyGenX evaluates BRAF, KRAS, HRAS, NRAS, and PIK3CA point mutations and RET-PTC and PAX8-PPARγ oncogene fusions, while ThyraMIR assesses the expression levels of 10 miRNAs.
In this study, we present the suitability and clinical utility of stained cytology smear slides, FFPE tissues, and related fixative-treated thyroid cell specimens for ThyGenX and ThyraMIR molecular testing. We demonstrate that both ThyGenX and ThyraMIR tests can be successfully carried out using total nucleic acid (TNA) obtained from these clinical thyroid specimens. The implications of these studies on the determination of various diagnostic and prognostic markers of thyroid malignancy is discussed.