The Absence of a Significant Role for β-Catenin in the Tumorigenesis of the Serrated Adenoma of the Colorectum : A Comparative Study with the Traditional Tubular Colorectal Adenoma

The nuclear accumulation of β-catenin due to adenomatous polyposis coli (APC) gene alterations plays a central role in the tumorigenesis of the traditional tubular adenoma (TA) through activation of the Wingless/Wnt signal transduction pathway. To determine whether β-catenin plays a role in the tumorigenesis of the serrated adenoma (SA), a newly proposed subtype of colorectal adenoma, we immunohistochemically evaluated the nuclear expression of β-catenin in SA compared with that of the traditional TA. Twenty-three samples of SA without familial adenomatous polyposis (FAP) and 24 samples of TA without FAP and TA with FAP were respectively examined. While nuclear β-catenin expression was demonstrated in 79% (19/24) of TAs without FAP and 91% (22/24) of TAs with FAP, that in SAs was 0% (0/23). The difference in the expression rate in TAs without and with FAP from that in SAs was significant (p<0.0001, respectively). These results indicate that the tumorigenesis of the SA is distinct from that of the traditional TA and that the SA does not follow a APC/β-catenin/ Wnt signaling pathway.