Immunohistochemical markers in the diagnosis of papillary thyroid carcinomas: The promising role of combined immunostaining using HBME-1 and CD56.

We aimed to evaluate the expression and diagnostic value of five immunohistochemical markers (HBME-1, Galectin-3, CK19, CD56 and p63) in a very large series of unequivocal papillary thyroid carcinoma (PTC) cases, including both the classic (CPTC) and the follicular variant (FVPTC). We performed an immunohistochemical analysis on a tissue micro-array of 204 PTCs (98 CPTCs, 90 FVPTCs, and 16 other variants). HBME-1 was the most sensitive marker, staining 95.9% of CPTCs and 81.1% of FVPTCs. CD56, a marker whose expression is reduced or absent in thyroid carcinoma, revealed a negative, "malignant" profile in 93.9% of CPTCs and 73.3% of FVPTCs. Galectin-3, CK19 and p63 were positive in 64.7%, 45.6% and 6.9% of PTCs, respectively. The immunopanel consisting of HBME-1, CD56 and/or CK19 reached the highest sensitivity (95.6%). The co-expression of 2 or more proteins was observed in 88.2% of PTCs, with HBME-1 and CD56 being the most frequent positive association (79.4%). We report a new panel of antibodies consisting of HBME-1, CK19 and CD56 that was found to be highly sensitive for both CPTC and FVPTC. This panel could be recommended as a supplement to the morphological criteria in the diagnosis of difficult FVPTC cases.