Cyclin-dependent kinase (cdk6) and p16 in pancreatic endocrine neoplasms

AIMS: p16 and p27, the inhibitors of cyclin-dependent kinases, have been reportedly decreased in certain human tumours, including a few endocrine tumours. The current study used immunocytochemical staining to compare the staining intensity of cdk6 and its inhibitor, p16, in pancreatic endocrine neoplasms with normal pancreatic islets. METHODS: Twenty-four primary pancreatic endocrine neoplasms, consisting of 12 insulinomas, one glucagomoma, three pancreatic polypeptide (PP)-omas, five gastgrinomas and three non-fuctioning tumours, were immunocytochemically studied for cdk6 and p16 compared with the adjacent non-neoplastic islets. RESULTS: In the normal islets, cdk6 staining was strongly positive for islet cell nuclei and cytoplasms, whereas p16 was strongly positively stained for islet cell cytoplasms. Insulinomas, glucagonoma, PP-omas and non-functioning tumours were weakly stained for cdk6 and p16. Among five gastrinomas, three tumours were moderately stained and two tumours were more weakly stained for cdk6 and p16. Thus, tumour cells were weaker stained for cdk6 and p16 compared with the strong staining of normal islet cells. No distinct immunostaining difference was observed among five kinds of pancreatic endocrine neoplasms. CONCLUSIONS: The decreased immunocytochemical staining for cdk6 and p16 is consistently observed in five kinds of pancreatic endocrine neoplasms. This decreased cdk6 and p16 in pancreatic endocrine neoplasms may be a part of the cell cycle event in tumour transformation and progression, and the same process may involve other endocrine tumours.