The Role of pRB, p16 and Cyclin D1 in Colonic Carcinogenesis

Background/ Aims: This study is aimed to investigate abnormal expression of the Rb protein (pRb), p16(INK4n) (p16) and cyclin D1 in colorectal adenomas and adenocarcinomas and to assess the possible alterations in Rb pathway in colorectal carcinogenesis. METHODOLOGY: 44 cases of colorectal adenoma and 44 cases of colorectal adenocarcinoma were examined histopathologically and immunohistochemically using monoclonal antibodies to identify abnormalities of pRb, p16, and cyclin D1 expression. Staining degree of above-mentioned markers was assessed by using a semi-quantitative method in all cases in order to determine any staining differences. RESULTS: In 70.5% of the adenomas and 97.7% of the adenocarcinomas, an overexpression of pRb was found. There was a statistically significant relationship between the immunoreactivity of pRb and villous/ tubulovillous types of adenomas (p<0.05). There was a loss of p16 expression in 84.1% of adenomas and 61.4% of adenocarcinomas. Statistically significantly, the p16 overexpression was not seen in any of tubular adenomas (p<0.001). Overexpression of cyclin D1 was found in only 9.1% of adenomas, while 31.8% of adenocarcinomas overexpressed this protein. Loss of expression of cyclin D1 was similar in adenomas and adenocarcinomas (27.3% and 25%, respectively). Staining degrees of all three cell cycle proteins were shown to be statistically different in adenomas and adenocarcinomas, for pRb (p=0.001), for p16 (p=0.045), and cyclin D1 (p=0.05). Also, there was only a mild agreement with respect to p16 and cyclin D1 relationship between for adenomas (k=+0,28 p=0,051) and for adenocarcinomas (k=+0,35 p=0,017). Besides, there was no correlation between the expression of pRb, p16, and cyclin D1 and clinicopathological tumor characteristics and prognostic data such as stage or lymph node/liver metastasis. CONCLUSIONS: pRb, p16 and cyclin D1 are shown to be aberrantly expressed in both colorectal adenomas and adenocarcinomas. It can be claimed that disturbances in Rb pathway take part in colonic carcinogenesis and pRb, p16 and cyclin D1 play an ever increasing role in the further stages of adenoma-carcinoma sequence.