RAD51 is the central protein in the homologous recombination pathway and is therefore of great relevance in terms of both therapy resistance as well as genomic stability. By using a tissue microarray analysis of 1,213 biopsies taken from colorectal adenocarcinomas (CRCs), we investigated whether RAD51 expression can be used as a prognostic marker as well as potential associations between this and the expression of other proteins known to be related to CRC. Strong RAD51 expression was observed in 1% of CRC, moderate in 11%, weak in 34% and no expression in 44%. No correlation was found between RAD51 expression and clinicopathological parameters. RAD51 expression correlated significantly (p 5 0.001) with overall survival, with a median survival of 11 months for patients with strong, 46 with moderate, 76 with weak and 68 with negative expression. Multivariate analyses revealed that in addition to tumor stage (p < 0.0001) and nodal status (p < 0.0001), RAD51 expression is also an independent prognostic parameter (p 5 0.011). Strong RAD51 expression was found to be associated with the loss of the two DNA mismatch repair proteins MSH (p 5 0.0003), MLH (p 5 0.002) and b-catenin (p 5 0.012) as well as with elevated p21 (p 5 0.003) and EGFR expression (p 5 0.0001). However, a correlation with overall survival could only be found for EGFR expression (p 5 0.008), although no added benefit in risk stratification could be determined when evaluated together with RAD51. Overexpression of RAD51 is a predictor of poor outcome in CRC. This finding indicated the promise of future studies using RAD51 as a prognostic marker and therapeutic target.Colorectal cancer (CRC) is one of the most frequent cancers, with over 1 million new cases worldwide each year and a disease-specific mortality of 33-40%.

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