Molecular Diagnostics in Thyroid Cytopathology

Abstract

Molecular testing of thyroid specimens has increased dramatically over the last decade and has become an important adjunct to cytopathology for the management of patients with thyroid nodules. Current applications include tumor subtyping, tumor prognosis, and risk stratification of specific subtypes of thyroid nodules. Among these applications, the latter has shown the most significant clinical utility and adoption. Specifically, this application involves the molecular analysis of thyroid fine needle aspiration (FNA) specimens from indeterminate nodules that are not clearly benign or malignant cytologically and carry an elevated risk of malignancy (ROM) relative to cytologically benign nodules. Because of this unacceptably high ROM, patients with indeterminate nodules frequently undergo diagnostic surgery although approximately 75% of the nodules are found to be histologically benign upon surgical pathology review. The goal of molecular testing of these indeterminate nodules, which comprise approximately 15–30% of all cases, is to reclassify them into lower or higher risk groups, permitting conservative management and unnecessary surgery in the lower risk group while increasing the chance of malignancy and potentially guiding surgical management in the higher risk group. The aim of this chapter is to provide an overview of the current and future uses of molecular testing of thyroid cytopathology specimens with a focus on molecular evaluation of those with indeterminate cytopathology.