44 - Thyroid Cancer

Abstract

Thyroid cancer (TC) has increased worldwide in the last three decades, most likely owing to diagnosis of small low-risk papillary thyroid cancers (PTCs). Unlike other cancers, TC usually has a favorable prognosis with regard to overall survival because 84% of all TCs are PTCs with low-mutation burden and mostly good outcomes. TCs that originate from the follicular cell are differentiated thyroid cancers (DTCs) including PTCs, follicular thyroid cancers (FTCs), Hürthle cell carcinomas (HCCs), and poorly differentiated thyroid cancer (PDTCs); and undifferentiated or anaplastic thyroid cancer (1%). Medullary thyroid cancer (MTC) derives from the C-cells. Recently the World Health Organization (WHO) updated their histologic classification of endocrine tumors with unique new features, such as consideration of FTCs and HCCs as different TCs because of distinct biologic and clinical behavior as well as the recognition of a unique follicular-derived neoplasm termed “noninvasive follicular thyroid neoplasm with papillary-like nuclear features (NIFTP),” which was previously considered cancer (encapsulated noninvasive follicular-variant of PTC). Other major updates in the TC field have been (1) the genomic characterization of PTCs and PDTCs or anaplastic thyroid cancers (ATCs), with an increased frequency of somatic gene mutations in the latter, consistent with their more aggressive behavior; (2) the American Joint Committee on Cancer (AJCC/TNM) (primary tumor, regional nodes, metastases) eighth edition resulted in major changes for TC, leading to downstaging of a considerable number of patients with DTC; and (3) an other major achievement has been the approval of different targeted therapies (kinase inhibitors) for TC patients with advanced and rapidly progressive disease.