Cytoplasmic CD133 Expression is a Reliable Prognostic Indicator of Tumor Regression After Neoadjuvant Concurrent Chemoradiotherapy in Patients with Rectal Cancer

Despite development in therapeutic strategies, such as neoadjuvant concurrent chemoradiotherapy (CCRT), the prognosis of colorectal cancer remains relatively poor. Cancer stem cells (CSC) with several characteristics can lead to therapeutic resistance. CD133 has been identified as a putative CSC marker in colorectal cancer; however, its functional role still needs elucidation. We verified the role of CD133 with emphasis on expression location and correlated the results of CD133 with clinical outcome in colorectal cancer. We used immunohistochemistry to investigate the expression of CD133 in samples from 157 patients with colonic adenocarcinoma and from 76 patients with rectal adenocarcinoma who received neoadjuvant CCRT. We also correlated the expression location of CD133 with the clinicopathological parameters and prognosis. CD133 protein was variably overexpressed in colorectal cancer tissues and was present in three locations: apical and/or endoluminal surfaces, cytoplasm, and lumen. Cytoplasmic CD133 expression level correlated significantly with tumor local recurrence (P = 0.025) and survival of patients with colorectal cancer (P = 0.002), and correlated inversely with tumor regression grading (P = 0.021) after CCRT in patients with rectal cancer. The expression of CD133 in the cytoplasm is closely associated with local recurrence and patient survival, and may provide a reliable prognostic indicator of tumor regression grading in patients with rectal cancer after CCRT. Cytoplasmic CD133 expression may also help identify the surviving cancer cells in areas with nearly total regression after CCRT.