Objectives: Cyclins play an important role in the regulation of cell progression through the cell cycle. Over-expression of the cyclins has been shown in many different tumour types. Pituitary adenomas are a common form of endocrine neoplasia in the human, but have been little studied in terms of the expression of the principal cyclins regulating checkpoint exit, cyclin D1 and cyclin E. Methods: We therefore investigated the expression of cyclin D1 and cyclin E in a range of benign and metastatic pituitary tumours. We studied a total of 95 pituitaries, including normal pituitary (n = 20), Cushing's disease (n = 19), somatotroph tumours (n = 19), non-functioning adenomas (n = 18), prolactinomas (n = 7), aggressive tumours (n = 9) and pituitary carcinoma (n = 3). All tumours and normal tissue were immunostained for cyclin D1 and cyclin E using a standard technique, and were then subjected to blinded analysis by a single observer and the extent of staining quanti®ed on the basis of 500 cell counts per tissue. The distribution of positive staining between different tissues was analysed by non-parametric test procedures. Results: There was no cytoplasmic staining for cyclin D1 in any tissue. Nuclear staining was generally sparse, but was statistically more frequent in non-functioning and aggressive tumours compared with other tumour types or normal pituitary. Cyclin E was also sparsely expressed, but was speci®cally increased in corticotroph tumours from patients with Cushing's disease. Conclusions: We report cyclin D1 over-expression in aggressive and non-functioning pituitary tumours, and that cyclin E espression is more frequently seen in Cushing's disease. The high level of cyclin E expression in Cushing's disease may relate to the low level of p27 protein expression previously reported in corticotroph tumours.

The cell cycle is regulated by a number of inhibitors, including p27Kip1 (p27), which belongs to the kip1 family. By binding to the cyclin/cyclin-dependent kinase complexes, it regulates progression of G1 to S phase in the cell cycle. It has been reported that p27 knockout mice develop multiorgan hyperplasia and intermediate lobe pituitary tumors secreting ACTH. Previously, we and others have been unable to show any consistent change in messenger RNA expression or genomic mutations for p27 in human corticotroph adenomas. However, dysregulation at the protein level has been reported in nonendocrine tumors, and we, therefore, investigated the expression of p27 in a range of benign and metastatic pituitary tumors. We studied a total of 107 pituitaries, including normal pituitary (n = 20), Cushing's disease (n = 21), acromegaly (n = 19), nonfunctioning adenomas (n = 18), prolactinomas (n = 7), TSH-omas (n = 2), FSH-omas (n = 6), aggressive tumors showing invasiveness and recurrence (n = 9), and metastatic pituitary carcinomas (n = 5). Using standard immunohistochemical techniques with a highly specific monoclonal antibody, p27 expression was determined quantitatively as the percentage of cells showing strongly positive, weak, or negative staining. In each sample, approximately 500 cells were analyzed. We also analyzed normal pituitaries using double-labeling for p27 and each of the pituitary hormones to characterize the expression of p27 in each cell type. p27 was expressed in normal pituitary cells; in tumors expressing GH, prolactin, TSH, and FSH; and in aggressive tumors, but markedly reduced expression of p27 was seen in corticotroph tumors and pituitary carcinomas. In the normal pituitary, somatotroph, lactotroph, and thyrotroph cells showed strong p27 staining, whereas normal corticotroph cells showed a much lower level of p27 staining (P < 0.001). Somatotroph, lactotroph, gonadotroph, and thyrotroph adenomas showed a lower level of p27 expression compared with normal somatotrophs (P = 0.02), lactotrophs (P = 0.03), gonadotrophs (P = 0.01), and thyrotrophs, respectively, whereas the lower level of p27 expression present in normal corticotrophs virtually disappeared in corticotroph adenomas (P = 0.001). We conclude that pituitary adenomas show a lower level of p27 protein expression than the normal cells from which they are derived, with malignant transformation leading to complete loss of p27 immunoreactivity. Corticotrophs are quite different to other pituitary cell types in terms of p27 immunoreactivity because both normal and tumorous corticotrophs have low p27 staining, and we speculate that this may relate to their inherent control mechanisms.