c‐FLIP expression in colorectal carcinomas: association with Fas/FasL expression and prognostic implications

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Abstract
Disruption of apoptotic cell death has been implicated in tumour aggressiveness in colonic carcinogenesis. The Fas-Fas ligand (FasL) system is involved in the execution of apoptosis induced by the immune system. c-FLIP protein constitutes an inhibitor of Fas and other (TRAIL) death receptor-mediated apoptosis. The aim of this study was to investigate the simultaneous expression of Fas, FasL and c-FLIP in relation to standard clinicopathological parameters and patients' outcome in colorectal cancer. Levels of Fas, FasL and c-FLIP protein expression were quantified immunohistochemically in paraffin-embedded tissues from 90 patients. Immunopositivity was detected for Fas, FasL and c-FLIP in 71%, 35.5% and 68.8% of cases, respectively. Concurrent expression of Fas/FasL was seen in 28 samples (31%), of which 24 (85.7%) also displayed c-FLIP positivity (P = 0.04). c-FLIP overexpression (> 10%) tended to prevail marginally in higher stage tumours (P = 0.09). Additionally, FasL and c-FLIP adversely affected survival on both univariate (P = 0.001 and P = 0.0024, respectively) and multivariate analysis [hazard ratio (HR) 3.491, P = 0.005 and HR 2.960, P = 0.036, respectively]. The frequent expression and coexpression of Fas, FasL and c-FLIP in colorectal carcinoma implicates c-FLIP as an inhibitor of the Fas-FasL-induced death pathway in these tumours. Moreover, c-FLIP conveys independent prognostic information in the presence of classical prognosticators.