Alterations in the retinoblastoma pathway of cell cycle control in parathyroid tumors.

Mutations in proto-oncogenes and tumor suppressor genes have been associated with tumor development and/or progression in many neoplasms. It has been reported that parathyroid tumors have deletions affecting the retinoblastoma gene (RB), and overexpression of cyclin D1 (Cyc D1). The aim of the present study was to evaluate the alterations in the components of the pRB pathway in parathyroid adenomas and parathyroid aggressive tumors, including patterns of expression of pRB, Cyc D1, and p16/INK4A. Paired normal and tumor DNA from 6 parathyroid adenomas and 5 aggressive tumors were analyzed for loss of heterozygosity (LOH) at the RB locus. The expression of pRB, Cyc D1 and p16 was studied in 4 adenomas and 5 aggressive tumors. RB LOH was found in 1 of 6 adenomas, and in 1 of 2 informative aggressive tumors. Immunohistochemical analysis revealed undetectable pRB in 4 of 5 aggressive tumors and presence of pRB in all adenomas. Conversely, Cyc D1 expression was found in 3 of 4 aggressive tumors, but was undetectable in the adenomas. Expression of p16 was identified only in one aggressive tumor. Thus, alterations in the pRB pathway seem to prevail in the aggressive form of parathyroid neoplasms. Our results warrant further investigation of these cell cycle regulators in order to determine their potential role as tumor markers in parathyroid tumors.