Abstract
Simple SummaryThyroid tumors that derive from follicular cells are not a homogeneous entity, showing variable morphological appearance and different degrees of differentiation. Molecular markers are useful for both diagnostic purposes and prognostic stratification of patients. In presurgical setting, molecular testing of indeterminate thyroid nodules on aspirates provides useful diagnostic information; the molecular analysis on tumor tissues can also reveal the presence of genetic alterations related to patients’ prognosis. In recent years, the molecular characterization of these tumors has acquired even more importance thanks to the introduction of targeted drugs. This review summarizes the current literature on the molecular landscape of follicular-derived thyroid tumors.Thyroid cancer is the most common type of endocrine-related malignancy, whose incidence rates have increased dramatically in the last few decades. Neoplasms of follicular origin generally have excellent prognosis, with the exception of less differentiated tumors. Follicular-derived thyroid cancer can manifest as a variety of morphologically distinct entities, characterized by various degrees of differentiation and invasiveness. Histological evaluation is thus crucial for the definition of patients’ prognosis. However, within each histological subtype, tumor behavior can be highly variable, and, in this respect, molecular characterization can provide insightful information to refine the risk stratification of tumors. In addition to the importance of its prognostic role, molecular testing can be used to support the differential diagnosis of thyroid nodules in the absence of marked cyto-morphological aberrations. Finally, with the advent of targeted drugs, the presence of molecular alterations will guide the therapeutic strategies for patients with advanced tumors who do not respond to standard treatment. This review aims to describe the genetic landscape of follicular-derived thyroid tumors also highlighting differences across histological subtypes.
Highlights
Thyroid tumors originated from follicular cells, namely non-medullary thyroid cancers, encompass 95% of all thyroid malignancies [1]
A primary gross distinction can be made between well-differentiated thyroid carcinomas (WDTC), which include papillary thyroid carcinomas (PTC), follicular thyroid carcinomas (FTC), and Hürthle cell thyroid carcinomas (HCC), and less differentiated forms, i.e., poorly differentiated thyroid carcinomas (PDTC) and anaplastic, or undifferentiated, thyroid carcinomas (ATC)
Since TERT promoter mutations show a higher frequency in morphologically aggressive WDTCs such as tall cell PTCs and widely invasive HCCs, they can contribute in part to the evidence demonstrating their association with poor patient prognosis
Summary
Thyroid tumors originated from follicular cells, namely non-medullary thyroid cancers, encompass 95% of all thyroid malignancies [1]. BRAFV600E-like alterations include mutations other than the BRAFV600E ones, as for example RET/PTC and BRAF fusions These alterations are associated with a papillary architecture and a lower expression of thyroid-differentiation genes. RAS-like alterations (including RAS mutations, the BRAFK601E mutation, PPARG fusions, THADA fusions and EIF1AX mutations) are associated with a follicular architecture and a close-to-normal expression of the genes related to thyroid differentiation [9] The identification of this fundamental, deep distinction between CPTCs and FVPTCs has led many authors to wonder whether BRAF-like and RAS-like definitions could be extended to the other thyroid tumors. Since TERT promoter mutations show a higher frequency in morphologically aggressive WDTCs such as tall cell PTCs and widely invasive HCCs, they can contribute in part to the evidence demonstrating their association with poor patient prognosis. Secondary mutations in NIFTP have been rarely described, confirming that their morphologically and clinically indolent nature is accompanied by a relatively low-risk molecular profile
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