Immunohistochemical Analysis of the Cell Cycle-Associated Antigens Ki-67 and Retinoblastoma Protein in Parathyroid Carcinomas and Adenomas

The morphologic distinction between parathyroid carcinoma and adenoma can be a difficult diagnostic problem. We analyzed nuclear immunoreactivity for the cell cycle-associated antigen Ki-67 with monoclonal antibody (MAb) MIB-1 and for retinoblastoma (RB) protein with two polyclonal antisera in 24 parathyroid carcinomas and 35 adenomas, which were formalin fixed and paraffin embedded to determine if these antibodies could assist in distinguishing between carcinomas and adenomas. In addition, 10 cases of parathyroid hyperplasia and 5 cases of normal parathyroids were examined as control tissues. The Ki-67 labeling index was significantly higher in parathyroid carcinomas compared to adenomas (7.1 ± 1.0% vs 2.4 ± 0.2%,p<0.001). No patient with a parathyroid adenoma, parathyroid hyperplasia, or normal parathyroid gland had a Ki-67 labeling index >5.3%. Analysis of the primary tumors from patients with recurrent carcinomas and from those with nonrecurrent carcinomas showed a higher mean Ki-67 labeling index (7.8 ± 1.5% vs 5.2 ± 1.1%), in the former group, although these differences were not statistically significant. The RB protein immunoreactivity was not useful in distinguishing between parathyroid carcinomas and adenomas in paraffin-tissue sections. These results indicate that nuclear immunoreactivity for the cell cycle-associated antigen Ki-67 may be another useful method to assist in distinguishing parathyroid carcinomas from adenomas.