Loss of heterogeneous ribonucleoprotein A(2)/B(1) expression in thyroid neoplasms

To determine whether a difference exists in the immunohistochemical expression of heterogeneous ribonucleoprotein (hnRNP) A(2)/B(1) between benign and malignant thyroid lesions and to assess whether a gradient of expression could be found in normal thyroid, adenomas, and thyroid malignant tumors.

Formalin-fixed, paraffin-embedded archival tissues from 32 cases (8 nodular goiters, 8 follicular adenomas, 8 follicular carcinomas, and 8 papillary carcinomas) were immunostained with monoclonal antibody 703D4, directed against hnRNP A(2)/B(1), applied at a concentration of 10 microg/mL. The streptavidin-biotin peroxidase method was used to label bound monoclonal antibody. Positivity was independently scored by two pathologists, who used a three-tiered scale.

The benign thyroid tissues, including the hyperplastic and adenomatous lesions, demonstrated 3+ granular cytoplasmic staining for hnRNP A(2)/B(1), except in two cases (one nodular goiter and one follicular adenoma) in which 2+ staining intensity was noted. In contrast, the papillary and follicular carcinomas failed to stain with the antibody, except in two cases that showed weak (1+) staining.

hnRNP A(2)/B(1) immunostaining appears to distinguish benign from malignant thyroid lesions. Loss of hnRNP A(2)/B(1) expression seems to be a characteristic feature of thyroid malignant lesions.