β-catenin activation through mutation is rare in rectal cancer

Increased transcriptional activation through β-catenin stabilization plays a central role in colorectal tumorigenesis. Alterations of phosphorylation sites within the CTNNB1 gene, which codes for β-catenin has been reported to occur in about one-half of colorectal tumors without APC-gene mutations. We assessed the importance of mutations in the regulatory domain, located within exon 3 of CTNNB1, in 103 rectal carcinomas and correlated these data with presence of microsatellite instability, somatic frame-shift alterations of the TCF-4 gene, and APC-gene mutations in the tumors. No mutation was detected in exon 3 of the CTNNB1 gene and our results thus demonstrate that β-catenin activation through mutation rarely contributes to the development of sporadic and microsatellite instability stable rectal cancer.