Intranodal benign thyroid tissue: significance of HBME-1 in differentiation from metastatic papillary thyroid carcinoma

The aim of this study was to determine the significance of HBME-1 immunostaining in the differentiation between intranodal benign thyroid tissue and metastatic papillary thyroid carcinoma in the lymph node. Immunohistochemically we examined normal-appearing intranodal thyroid tissue in four patients who did not show evidence of papillary carcinoma histologically or clinically. We also examined follicular-pattern-predominant papillary carcinoma with metastatic foci in the lymph nodes. Normal-appearing intranodal thyroid tissue and normal thyroid showed no immunopositivity for HBME-1. In contrast, all papillary carcinomas in both the lymph nodes and thyroid demonstrated strong positivity for HBME-1. HBME-1 was predominantly positive for the luminal surface of the tumor cells. The immunopositivity of the cuboidal and low columnar carcinoma cells was more intensive than that of the flat-shaped cells in the lymph nodes and thyroid. The results probably indicate that HBME-1 immunostaining is helpful in distinguishing between intranodal benign thyroid tissue and metastatic papillary carcinoma in lymph nodes. We emphasize that the HBME-1 reactivity should be evaluated in connection with the histological findings, and that positive and negative controls stained in parallel are necessary.