[Prognostic factors of gastrointestinal stromal tumors of the stomach].

The stomach is the most common gastrointestinal site of mesenchymal tumors which traditionally have been designated as smooth muscle tumors. However, with increasing analytic tools most investigators were unable to demonstrate true myogenic differentiation. Furthermore, the biological behavior of gastrointestinal stromal tumors (GIST) is difficult to predict. The aim of this study was to evaluate MIB-1 and p53 as additional prognostic markers, as well as myogenic differentiation immunohistochemically in GIST. 43 gastric stromal tumors were reviewed, 19 were classified as benign, and 10 as malignant. 14 tumors were considered indeterminate for biological behavior. In addition to MIB-1 and p53, immunohistochemistry was also performed for sm-actin, desmin and S 100-protein (ABC). 41 patients had a clinical follow-up of more than 2.5 years, 5 patients had metastases. Mean proliferation rates defined as percentage of MIB-1 positive tumor cells in 3 HPF were as follows: typical leiomyoma: 0.2%; benign GIST, spindle cell type: 1.8%; benign GIST, epithelioid cell type: 2.4%; borderline GIST, spindle cell type: 2.1%; borderline GIST, epithelioid cell type: 2.5%; malignant GIST, spindle cell type: 4.9%; and malignant GIST, epithelioid cell type: 7.3%. All 5 metastasizing tumors had a proliferation index > 4% (p < 0.0001). 4/5 metastasizing tumors had p53 positive cells (p < 0.05). 36/43 tumors were sm-actin positive, 7 of which were positive for desmin as well. Classification of gastric mesenchymal tumors as GIST is appropriate because only a small percentage show true smooth muscle differentiation. A MIB-1 proliferation index above 4% might indicate a more aggressive course, as well as p53 positivity.