ABERRANT P27(KIP1) EXPRESSION IN ENDOCRINE AND OTHER TUMORS

The p27(kipl) (p27) gene encodes an inhibitor of cyclin-dependent kina se activity, The expression of p27 protein in normal and neoplastic ti ssues was investigated by immunoblotting and immunohistochemistry. Imm unoblotting studies detected a 27-kd protein band that was decreased i n neoplastic pituitary tissues compared with normal pituitary. Immunos taining of 177 tissues showed abundant expression of p27 protein in no rmal tissues with decreased numbers of immunoreactive cells in adenoma s and carcinomas in both endocrine and nonendocrine tissues, p27 expre ssion was inversely related to the proliferation marker Ki-67 antigen detected with monoclonal antibody MIB-1. Parathyroid adenomas and hype rplasias had similar Ki-67 labeling indices; however, hyperplasias had threefold more p27-positive cells than parathyroid adenomas, suggesti ng that p27 immunostaining may be useful in distinguishing between the se two conditions, These results indicate that there is widespread abe rrant p27 expression in hyperplastic tissues and in benign and maligna nt neoplasms compared with normal tissues, Immunohistochemical analysi s of p27 along with Ki-67 may be used to assess the biological behavio r of various neoplasms, to classify hyperplastic and neoplastic tissue s, and to study cell cycle regulation during tumor progression.