Evaluation of retinoblastoma and Ki-67 immunostaining as diagnostic markers of benign and malignant parathyroid disease

Assessment of the malignant potential of parathyroid tumors in the absence of metastases can be difficult using morphologic criteria alone. In this st udy we have examined a total of 58 parathyroid tumors (31 benign, 15 malign ant, and 12 equivocal) from 54 patients using immunohistochemistry with mon oclonal antibodies directed against the retinoblastoma (RB) protein and the cell cycle-associated antigen Ki-67 to evaluate their role as diagnostic m arkers. RE protein immunoreactivity was not useful for distinguishing betwe en benign and malignant parathyroid tumors. Analysis of the proliferation m arker Ki-67 showed that there was a trend toward more intense staining in t he malignant cases. The Ki-67 labeling index was highest in the parathyroid cancers (median 33) and lowest in the sporadic primary adenomas (median 2) . An observation that might have clinical implications is that tumors from patients with familial hyperparathyroidism linked to chromosome Iq showed a high Ki-67 index, indicating strong proliferative activity (median 25). Th is correlates well with the clinical observation of tumors with malignant p otential in this syndrome. Because of the considerable overlap between grou ps of tumors, Ki-67 is not suitable for definitive differentiation between benign and malignant tumors. However, Ki-67 may give valuable information a bout which patients should be followed more closely.