| Because the PRAD 1 , or cyclin D 1 , gene , a cell cycle regulator , has been implicated in a subgroup of benign parathyroid tumors , we examined the possibility that another cell cycle regulator with possible functional links to PRAD 1 , the retinoblastoma tumor suppressor gene ( RB ) , might be involved in the molecular pathogenesis of parathyroid carcinoma . ^^^ |