Introduction: Epithelial cell adhesion molecule (Ep-CAM) is a homophilic cell adhesion molecule expressed on the membranes of glandular epithelial cells, which is overexpressed by adenocarcinomas. This study investigates the contribution of Ep-CAM in progression and invasion of colorectal tumors Methods: Patterns of Ep-CAM staining were studied in colorectal adenocarcinomas, using 3 different antibodies: the epitope of monoclonal Ber-Ep4 is located at the N-terminal of the protein, monoclonal 311-1K1 binds to the extracellular domain in a more C-terminal fashion. The polyclonal antibody binds at intra- and extracellular epitopes. Expression of Ep-CAM mRNA was studied with mRNA in situ hybridization. Currently, possible proteolytic cleavage of Ep-CAM is studied with Western blot analysis. Staining patterns of Ep-CAM in 133 rectal cancer patients of a radomized clinical trial were correlated with prognosis using Kaplan Meier curves and log rank testing. Ep-CAM staining was scored as no reduction, reduction at the invasive front and reduction throughout the tumor. Results: Staining of the extracellular part of the Ep-CAM protein was reduced in isolated tumor cells and small cell clusters of the infiltrating front of diffuse growing carcinomas, but not in circumscript growing tumors. The loss of the extracellular epitope was accompanied by a cytoplasmatic staining with the polyclonal antibody and a homogenous expression of Ep-CAM mRNA, suggesting posttranslational modifications of Ep-CAM. The reduction of Ep-CAM staining was correlated with a poor prognosis; an increased risk on local recurrence (5-year 34% versus 13%, p = 0.02) and overall recurrence (73% versus 49%, p = 0.03). Conclusions: Posttranslational modification of Ep-CAM, predominantly seen in single cells and small cell clusters at the tumor front, results in a loss of the extracellular part of the protein. Cytoplasmic staining patterns indicate that Ep-CAM remnants are internalized. The absence of extracellular EpCAM may induce an increased migratory potential in these cell groups, and this may be responsible for the poor prognosis of these tumors.

[Proc Amer Assoc Cancer Res, Volume 46, 2005]