Immunohistochemical detection of CD133 is associated with tumor regression grade after chemoradiotherapy in rectal cancer

CD133 has been identified as a putative cancer stem cell (CSC) marker in various cancers including colorectal cancer. The relation between CD133 expression and biological characteristics of colorectal cancer remains to be clarified. Protein expression of CD133 was immunohistochemically evaluated in surgical specimens of 225 patients with colorectal cancer who were treated by surgery, as well as those of 78 patients with rectal cancer who received preoperative chemoradiotherapy (CRT) followed by curative resection. The correlation between CD133 expression and clinicopathological features, tumor recurrence and overall survival was analyzed in both populations. Among 225 colorectal cancers without CRT, 93 (41.3%) were positive for CD133 expression, which was enhanced in cases with advanced T stage and venous invasion. Moreover, CD133 was positive in 47 (60.3%) of 78 cases with CRT, which was significantly higher than the CD133-positive rate in non-CRT specimens (P = 0.05). Expression of CD133 was independently correlated with the histological tumor regression grade (P < 0.01). These results suggest that CD133 is not a distinctive colorectal CSC marker; expression of CD133 is suggested to be one of the key factors associated with resistance to CRT in colorectal cancer.