Diagnosis of parathyroid carcinoma using immunohistochemical staining against hTERT

The differential diagnosis of parathyroid carcinoma from benign adenoma is often difficult when its typical clinicopathological features are absent, even with the aid of various molecular markers. We recently demonstrated that telomerase activation through hTERT expression is a unique characteristic that is limited to parathyroid carcinoma and not seen in benign tumors. In the present study, we investigated hTERT expression in parathyroid tumors using immunohistochemistry in an attempt to determine its clinical utility. There was no evidence of immunoreactivity in the 4 normal parathyroid glands and the 18 typical adenomas. In contrast, one atypical adenoma stained positively and homogeneously, and the disease recurred three times clinically. All of the 6 carcinomas demonstrated a clear positive nuclear staining of hTERT. Every hTERT-positive tumor showed a high Ki-67 index, i.e., greater than 4%. Nucleolin, an hTERT-binding protein, was abundantly and homogeneously expressed in all specimens examined independent of the pathological diagnosis and hTERT or Ki-67 expression. Therefore, it is possible that immunostaining with an anti-hTERT antigen (NCL-L-hTERT) individually may distinguish parathyroid carcinoma from benign tumors.