p27(kip1) and Other Cell-Cycle Protein Expression in Normal and Neoplastic Endocrine Tissues

Endocrine tumors are often diagnostic challenges. Recent studies have suggested that proteins that regulate cell cycle may have diagnostic and prognostic utility in endocrine tumors. p27(kip1) (p27) is a cyclin-dependent kinase inhibitor that regulates the transition from the G1 to the S phase of the cell cycle. p27 and other cell-cycle proteins are becoming increasingly important in assessing the biologic behavior of endocrine neoplasms, classifying hyperplastic and neoplastic endocrine tissues, and in the progression of endocrine tumors. p27 appears to separate normal from neoplastic endocrine tissues and, in some cases, benign from malignant endocrine tumors. However, there is overlap in p27 expression among individual cases of benign and malignant tumors, and p27 has only limited prognostic utility in endocrine tumors compared to some epithelial tumors such as breast and prostate neoplasms. Thus, more effective molecular and cellular markers that can be used for diagnostic and prognostic purposes in endocrine pathology are needed.