Differentiated high grade thyroid carcinomas: Diagnostic consideration and clinical features

Background: Differentiated high-grade thyroid carcinomas (DHGTCs) are a new diagnostic entity most recently defined in the 2022 World Health Organization's (WHO) Classification of Endocrine and Neuroendocrine Tumors. This new entity has been minimally described in the literature, and additional cases classified as such are missing. Materials and methods: Cases of DHGTCs diagnosed at our institution from 2012 to 2022 were identified, and the following were reviewed: cytologic and histologic diagnoses, ancillary testing, immunohistochemical staining, treatments, and patient outcomes. Immunohistochemical staining for Ki67 was performed on selected cases lacking this immunostain. A systematic literature review of the English literature on DHGTCs from 2013 to 2023 was performed using PubMed and Embase. Results: Case cohort included 32 cases of DHGTCs, with an average age of 52.6 years (range 17–84 years) and a male:female ratio of 1.3:1. All cases underwent fine needle aspiration (FNA) and were categorized by The Bethesda System for Reporting Thyroid Cytopathology (TBSRTC) as follows: 14 cases as malignant (43.8 %), 10 as follicular neoplasm (31.3 %), 5 as atypia of undetermined significance (15.6 %), 2 as suspicious for malignancy (6.2 %), and 1 as non-diagnostic (3.1 %). The average tumor size was 5.15 cm, and most were papillary thyroid carcinoma (28, 87.5 %), with classic subtype being the most common. Twenty-one cases revealed tumor necrosis and the mitotic activity in lesions without necrosis averaged to 5.5 mitoses per 2 mm² (range 0–7). The average Ki67 proliferative index was 5.6 %. Extrathyroidal extension was seen in 17, angioinvasion in 21, lymphatic invasion in 7, and perineural invasion in 1 case. Foci of solid or trabecular growth were identified in five cases. Lymph node metastases at the time of diagnosis were noted in 10 cases and 7 demonstrated distant metastases or locoregional recurrence. To date, 25 patients are alive, and one has died from disease. Conclusions: Our institutional experience demonstrates that DHGTC is a rare, but aggressive thyroid tumor subtype that requires consideration in the setting of a well-differentiated thyroid neoplasm to appropriately assess for possible disease recurrence and determination of patient prognosis.