Alcian blue and epithelial membrane antigen are useful markers in differentiating benign from malignant papillae in thyroid lesions.

Immunohistochemistry for epithelial membrane antigen (EMA) and histochemistry for alcianophilic substances were performed in 17 cases of papillary thyroid carcinoma (PTC) and 11 cases of benign thyroid lesions showing papillary changes (7 diffuse hyperplastic goitres-Graves' disease; 4 colloid cystic goitres). In all PTCs the glycocalix of the cells lining the papillary structures was strongly positive with anti-EMA antiserum. Alcian blue pH 2.5 stain (AB 2.5) was also positive in 15 of these cases. In contrast, no cases of benign thyroid lesions showed AB 2.5 positivity in the cells lining the papillary structures and the positivity with anti-EMA antiserum, present in only 5 out the 11 cases, was focal and very weak. These results indicate that the presence and distribution of EMA and alcianophilic substances may be useful in distinguishing benign from malignant thyroid lesions containing papillae.