Down-Regulation of RKIP Predicts a Worse Outcome in Dukes B Colorectal Carcinoma. Is This Down-Regulation Due to Hypermethylation?
B Doyle, S Hagan, L Scott, J O'Sullivan, HE Mulcahy, K Sheehan, W Kolch. Beatson Institute for Cancer Research, Glasgow, United Kingdom; University of Glasgow, Glasgow, United Kingdom; St. Vincent's University Hospital, Dublin, Ireland
Background: Raf Kinase Inhibitor Protein (RKIP) is an inhibitor of the Ras-Raf-MAPK pathway. Down-regulation has been shown to be important in a number of common cancers, including colorectal carcinoma (CRC). Dukes B CRC represents a significant post-operative management challenge and additional biomarkers that give further information on prognosis would be useful. The mechanism of RKIP down-regulation is controversial. Some authors have suggested promoter hypermethylation as the mechanism. Pyrosequencing is recognised as the gold-standard in methylation analysis. Here we use pyrosequencing to examine RKIP promoter hypermethylation.
Design: A tissue microarray consisting of 211 cases of Dukes B CRC with matched normal tissue was stained with an antibody for RKIP. Expression level was scored using a semi-quantitative scoring system which divided samples into 3 groups (Negative, Weakly Positive and Strongly Positive). RKIP expression was correlated with survival and with traditional clinico-pathological parameters. Pyrosequencing was used to examine RKIP promoter methylation in 30 CRC and matched normal tissues.
Results: 97 patient samples showed strongly positive expression of RKIP, 100 showed weakly positive expression and 14 were negative. RKIP expression levels correlated significantly with survival (p=0.007) in this group of Dukes B CRC patients. Patients with the highest levels of RKIP expression had the best prognosis and those with the lowest levels of RKIP expression had the worst prognosis. This correlation was independent of traditional clinico-pathological parameters such as T-Stage and lympho-vascular invasion (LVI). Of the 30 CRC samples only one showed hypermethylation of the RKIP promoter as measured by pyrosequencing.
Conclusions: RKIP expression levels can sub-stratify patients with Dukes B CRC by prognosis. Importantly this difference was independent of whether the tumour was T3 or T4 and other clinico-pathological parameters such as LVI. RKIP could be a very useful addition to current methods for selecting high-risk Dukes B CRC patients who may benefit from closer post-operative monitoring and potentially adjuvant therapy. Promoter hypermethylation does not appear to be the mechanism of RKIP down-regulation and further study is required to identify the mechanism.
Monday, March 9, 2009 9:30 AM
Poster Session I Stowell-Orbison/Autopsy Award # 93, Monday Morning