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.