Expression of Wilms' Tumor Gene Product (WT1) in Gastrointestinal Mesenchymal Tumor

[Abstract] Introduction: Gastrointestinal stromal tumor (GIST) is one of the representative tumors of gastrointestinal mesenchymal tumor (GIMT). GIST is recognized as a malignant neoplasm, but it is difficult to predict its prognosis. Wilms tumor gene WT1 has been identified to play an etiological role in Wilms' tumor. Regarded as a tumor suppressor gene, WT1 has been found to have an oncogenic role in the analyses of various tumors. Recently, WT1 protein was also reported to be expressed in some mesenchymal tumors. In this study, we examined WT1 expression in GIMTs. Methods: Sixty-seven GIMTs were reviewed on the basis of histological and immunohistochemical features. WT1 expression and its association with prognostic indicators, including tumor location, tumor size, mitotic count, microscopical necrosis, Ki-67 labeling index, and metastasis in individual tumors were examined. In this study, we limitedly used GIST cases that were positive for c-kit. Results: The specimens consisted of 52 GISTs, five smooth muscle tumors (four cases of leiomyoma and one case of leiomyosarcoma), seven schwannomas, and three unclassified tumors. WT1 expression was observed in the cytoplasm of 41 (78.8%) cases of GIST. No WT1 expression was demonstrated in smooth muscle tumors or schwannomas. Cajal cells in normal intestinal tissue expressed c-kit but not WT1. A significant correlation between the score of WT1 expression in GIST and prognostic indicators including mitotic count was observed (p=0.034). Conclusion: WT1 expression in GIST could be useful in the differential diagnosis of GIMTs. In addition, WT1 expression may be associated with tumorigenesis and tumor progression of GIST.