Association of the expression of CD133 in locally advanced rectal cancer with tumor regression and survival after neoadjuvant radiochemotherapy.

Abstract

479 Background: CD133 has been described as a stem cell marker in colorectal cancer and is associated with higher tumorigenic potential and resistance to radiochemotherapy (RCT). In this study the expression of CD133 was evaluated in pre-treatment tumor biopsies and corresponding post-treatment surgical specimens of locally advanced rectal cancer patients undergoing multimodal therapy and was correlated to histopathological features and clinical follow-up. Methods: 97 patients with UICC II/III rectal cancer treated with preoperative 5-FU based RCT within the German Rectal Cancer Trials were investigated. Pre- and post-treatment CD133 expression levels were determined using immunhistochemistry and correlated with histopathologic parameters, tumor regression, tumor recurrence and disease-free survival (DFS). Results: As compared to pre-treatment biopsies we observed a significantly higher CD133 expression in post-treatment tumor specimens (p=0.01). There was, however, no correlation for both biopsies and tumor specimens between CD133 expression levels, pathological characteristics and survival. In matched analyses of corresponding biopsy/tumor pairs, patients with a decreased number of CD133 positive cells after preoperative RCT showed significantly lower post-treatment tumor stages (p=0.03) and higher histopathological tumor regression (p<0.01). Moreover, these patients had a significantly improved DFS in uni- (p<0.001) and multivariate analyses (p=0.001). Conclusions: CD133 expression displays a marker with prognostic and monitoring validity in rectal cancer patients. A decrease of the CD133 positive cell fraction in post-treatment tumor tissue is associated with a more favorable outcome after preoperative RCT.