Gastrointestinal mesenchymal tumors (GIMTs) are the most common mesenchymal tumors of the gastrointestinal tract. RCAS1 (receptor-binding cancer antigen expressed on SiSo cells) is a cancer cell-surface antigen and has been identified as a prognostic factor in several cancer types. It is thought that tumor cells escape immune attack by expressing RCAS1, which induces apoptosis in receptor-positive immune cells. The current study was designed to elucidate the histogenesis of these tumors by using various immunohistochemical markers, and identify parameters that will help to establish the criteria of malignancy in the GIMT. We also discuss the clinicopathological significance of RCAS1 expression in the diagnosis and prognosis of GIMTs. A total of 70 cases of GIMTs were reviewed. Immunohistochemistry was performed between 1990 and 2000, with the avidin-biotin-peroxidase complex method on 3 µm-thick sections of formalin-fixed paraffin-embedded specimens of GIMTs. Antibodies to the following antigens were used: KIT (CD117), CD34 α-SMA, Desmin, cytokeratin, S-100 protein, p53, and RCAS1. Recurrence-free survival analysis was done with Stat View-J 5.0 statistical packages. Univariate analysis for a recurrence-free prognosis demonstrated that antibody detection of p53 expression (p=0.0333) and expression of RCAS1 (p=0.0008) is correlated with a significantly higher potential of recurrence. On multivariate analysis, tumor size and RCAS1 expression were independently and inversely correlated with recurrence-free survival. The expression of RCAS1 has not previously been reported in GIMT; indeed, our study suggests that the expression of RCAS1 is correlated with recurrence not only in carcinomas, but also in mesenchymal tumors.

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