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.