Immunophenotypic Panel for Comprehensive Characterization of Aggressive Thyroid Carcinomas

Aggressive thyroid carcinomas—anaplastic (ATC) and poorly differentiated (PDTC)—are rare but highly lethal malignant entities. Their immunophenotypical characterization is still incomplete, and no standardized diagnostic algorithms have been used. Our study retrospectively analyzes 40 thyroidectomy cases as follows: 12 ATC and 28 PDTC from 2014 to 2024 by evaluating clinical data, histopathological aspects, molecular analysis for presence of BRAFV600E and TERTC228/250T mutations, as well as immunohistochemical expression of BRAFV600E, total BRAF, K-RAS, TERT, PAX-8, TTF-1, P53, and Ki-67. BRAFV600E was present in 70% of cases, with higher prevalence in ATC. Total BRAF correlated positively with K-RAS and TERT and negatively with BRAFV600E. TERT abnormal expression was highly prevalent in over 90% of cases, while loss of TTF-1 and PAX-8 is associated with anaplastic transformation. Ki-67 proliferative index had significantly higher values in ATC, thus supporting its role as a marker for aggressiveness. On univariate analysis, higher Ki-67 indices and lymph node invasion are independent predictor factors for the presence of metastases. However, on multivariate analysis, they both lose significance. Upon multivariate analysis, loss of TTF-1 and tumor necrosis were significant predictors for anaplastic histotype. Specific BRAFV600E immunohistochemistry may be a good screening tool for the BRAFV600E mutation. Molecularly, there is a relatively frequent association of the BRAFV600E mutation and TERTC228, mainly in the PDTC subgroup. Patterns of marker expression suggest that BRAF or RAF activation with subsequent loss of TTF-1 or PAX-8, TERT upregulation, and TP53 alteration are frequent occurrences in aggressive thyroid carcinomas. The association between TTF-1 loss and anaplastic transformation, presence of necrosis alongside BRAFV600E, underlines their diagnostic potential in subclassifying aggressive thyroid carcinomas.