Background & Aims: Colorectal cancer represents the third most common malignancy and the fourth most common cause of cancer death worldwide. The existence of drug-resistant colon cancer stem cells is thought to be one of the most important reasons behind treatment failure in colon cancer, their existence putatively leading to metastasis and recurrences. The aim of our study was to investigate the immunoexpression patterns of CD133 and CD166 in colon carcinoma, both individually and in combination, assessing their significance as prognostic markers.Methods. A total of 45 retrospective colon adenocarcinoma cases were investigated by enzymatic and multiple fluorescence immunohistochemistry for their CD133 and CD166 expression and colocalization.Results. Both CD133 and CD166 were expressed to different extents in all cancer specimens, with apredominant cytoplasmic pattern for CD133 and a more obvious membranous-like pattern for CD166.Overall, when comparing their reactivity for the tumoral tissue, CD166 expression areas seemed to be smaller than those of CD133. However, there was a direct correlation between CD133 and CD166 expression levels throughout the entire spectrum of lesions, with higher values for dysplastic lesions. Colocalization of CD133/ CD166 was obvious at the level of cells membranes, with higher coeficients in high grade dysplasia, followed by well and moderate differentiated tumours.Conclusions. CD133/CD166 colocalization is an early event occurring in colon tumorigenesis, with thehighest coeficients recorded for patients with high grade dysplasia, followed by well differentiated tumours. Thus, we consider that the coexpression of these two markers could be useful for further prognostic andtherapeutically stratification of patients with colon cancer.Abbreviations: AJCC - American Joint Committee on Cancer; CCD - charge-coupled device camera sensor; CD133 - prominin-1 (PROM1); CD166 - Activated Leukocyte Cell Adhesion Molecule (ALCAM); CRC - colorectal cancer; CSC - cancer stem cells; DAB - 3,3'-diaminobenzidine chromogen; DAPI - 4',6-diamidino- 2-phenylindole; HE - Hematoxylin and eosin staining; HGD - high grade dysplasia; HRP - horseradish peroxidase; LGD - low grade dysplasia; SDS - sodium dodecyl sulfate*Part of this work has been accepted as a poster presentation at the Digestive Disease Week (DDW) meeting, Chicago, IL, USA May 3-6, 2014
