Molecular Characterization of Thyroid Follicular Lesions in the Era of “Next-Generation” Techniques

Abstract

It is unequivocally recognized that thyroid nodules are frequently detected in the adult population and mostly characterized by benign lesions (up to 70% of them), with only 5%–15% malignant lesions. The evaluation of thyroid lesions with fine-needle aspiration cytology (FNAC) represents one of the first and most useful diagnostic tools in the definition of their nature. Despite the fact that the majority of thyroid lesions are correctly diagnosed as either benign (70%–75%) or malignant (5%–10%) entities, the remaining nodules (20%–25%) represent the “gray zone” of follicular lesions, which belong to indeterminate categories, according to the different classification systems. This indeterminate group of lesions includes both benign and malignant entities, which cannot be easily discriminate with morphology alone. In these last decades, the increasing role of molecular testings, feasibly performed on cytological material combined with the discoveries of specific genetic alterations in the field of thyroid pathology, has opened the pace to their more accurate and specific contribution on cytology. In fact, in 2015, in the revised management guidelines for patients with thyroid nodules and well-differentiated thyroid cancers (WDTCs), the American Thyroid Association (ATA) confirmed the performance of molecular testing in thyroid indeterminate cytology, and the same performance was addressed in recent update of the management of thyroid nodules in the second edition of the Bethesda system for reporting thyroid cytopathology (TBSRTC). In the current review, we discuss the role of molecular tests for the different thyroid diagnostic categories of the Bethesda system for reporting thyroid cytopathology, mostly focusing our attention on the follicular and indeterminate lesions.

Diagnostic performance of C-TIRADS in malignancy risk stratification of thyroid nodules: A systematic review and meta-analysis

“…FNA molecular testing is a new approach that may reduce the need for diagnostic surgery ( 35 ). Targeted next-generation sequencing analysis of cancer-related genes for point mutations, gene fusions, copy number alterations, or abnormal gene expression is among the tests developed for this purpose ( 36 ). However, molecular testing should unquestionably be taken into consideration if clinical, imaging, and cytology results are insufficient for diagnosis and surgery is the only diagnostic option ( 5 , 37 ).…”

The basics of commonly used molecular techniques for diagnosis, and application of molecular testing in cytology

“…Additionally, the similarity of these cell blocks to traditional histology blocks means that a molecular assay previously validated for using FFPE samples will also be validated for using cell blocks. 4,[6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22] However, cell blocks have limitations similar to traditional FFPE samples.…”

“…These cell blocks can generate multiple sections, allowing for diagnostics slides to be retained while providing material for molecular testing. Additionally, the similarity of these cell blocks to traditional histology blocks means that a molecular assay previously validated for using FFPE samples will also be validated for using cell blocks 4,6–22 . However, cell blocks have limitations similar to traditional FFPE samples.…”

“…For instance, molecular testing in cytologically indeterminate thyroid nodules can help further risk‐stratify these nodules. Afirma (Veracyte, Inc.) and Thyroseq (University of Pittsburgh Medical Center, Pittsburgh, PA, and CBLPath, Inc.) assays are widely used commercially available molecular tests for this indication 9–11 . NGS‐based molecular testing has been applied in cytology samples obtained by endobronchial ultrasound‐guide fine needle aspiration (EBUS‐FNA) to molecular profile non‐small cell lung cancer (NSCLC) to detect potentially actionable mutations in select patients 10,12–18 .…”

“…Afirma (Veracyte, Inc.) and Thyroseq (University of Pittsburgh Medical Center, Pittsburgh, PA, and CBLPath, Inc.) assays are widely used commercially available molecular tests for this indication. 9 , 10 , 11 NGS‐based molecular testing has been applied in cytology samples obtained by endobronchial ultrasound‐guide fine needle aspiration (EBUS‐FNA) to molecular profile non‐small cell lung cancer (NSCLC) to detect potentially actionable mutations in select patients. 10 , 12 , 13 , 14 , 15 , 16 , 17 , 18 The same samples can also be utilized to perform PD‐L1 immunocytochemistry to select and predict immunotherapy treatment response.…”