Differentiated high-grade thyroid carcinoma (DHGTC): clinicopathological analysis of a new entity in a chilean center.
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INTRODUCTION: High-grade differentiated thyroid carcinoma (DHGTC) is a rare cancer with an intermediate behavior between well-differentiated thyroid carcinoma (WDTC) and anaplastic thyroid carcinoma. In 2022, the WHO defined DHGTC by the presence of ≥ 5 mitoses per 2 mm² and/or tumor necrosis in tumors that retain the morphological and immunohistochemical features of carcinomas derived from follicular thyroid cells. OBJECTIVES: To report the clinicopathological characteristics and outcomes of patients with DHGTC treated at a national center. DESIGN: Retrospective observational study. METHODS: Thirty-two patients with a confirmed diagnosis of DHGTC were included. The extent of surgery was defined according to thyroid fine-needle aspiration (FNA) and preoperative imaging, and the need for additional therapies based on histology, imaging, and postoperative thyroglobulin (Tg). Clinicopathological variables and follow-up every 6 months with neck ultrasound, Tg, and anti-Tg antibodies (TgAb) were recorded. RESULTS: Of the 32 patients, 27 (84.4%) were women, with a mean age of 39.8 ± 15.6 years and a median tumor size of 2.0 cm (range 0.5-6.0). Ultrasound was ACR-TIRADS 3, 4, and 5 in 3 (9%), 8 (26%), and 20 (65%) patients, and FNA resulted in Bethesda III-IV and V-VI in 8 (26%) and 23 (74%) cases, respectively. Eleven (34.4%) patients were treated with total thyroidectomy (TT), 11 (34.4%) with TT and lymph node dissection, and 10 (31.3%) with lobectomy (of these, 5 (50%) underwent completion thyroidectomy after histology was known). Twenty-seven (84.4%) had papillary thyroid carcinoma (PTC) and 5 (15.6%) follicular thyroid carcinomas (FTC). Among PTCs, 10 (37%), 5 (18.5%), 4 (14.8%), 3 (11.2%), and 5 (18.5%) were tall cell (TC), solid, classic, follicular, and other subtypes, respectively. Twenty-three (72%) had only ≥ 5 mitoses, 6 (18.6%) had only necrosis, and 3 (9.4%) had both (median mitosis count 6.5; range 5–11). In univariate analysis, male sex, age, and tumor diameter were associated with distant metastasis. Radioiodine was indicated in twenty-seven (84.4%) patients, of which 25 (77.7%) received a median dose of 50 mCi (range 30–200). According to AJCC 8, 28 (87.6%), 2 (6.2%), and 2 (6.2%) were stage I, II, and IVb, respectively. Thirty (93.7%) were followed for more than one year (median 2.3 years, range 1.91–6.92 years). At the end of the follow-up, all were alive, 19 (63.4%) had an excellent response, 6 (20%) had an indeterminate biochemical response, 3 (10%) had an incomplete biochemical response, and 2 (6.6%) had an incomplete structural response due to pulmonary metastases. CONCLUSIONS: DHGTC is rare, but its frequency will likely increase following the WHO publication. In our series, most cases correspond to PTC, with a high frequency of aggressive subtypes. After a median follow-up of 2.3 years, there were no deaths, and two patients had an incomplete structural response. Larger studies and longer follow-ups are needed to understand this disease’s behavior and personalize its management.