Gastrointestinal stromal tumors gists are soft tissue sarcomas that can be located in any part of the digestive system their most common sites are the stomach and small intestine gists start in specialized nerve cells located in the walls of your digestive system these cells are part of the autonomic nervous system. Gastrointestinal stromal tumors gists are the most common mesenchymal neoplasms of the gastrointestinal tractgists arise in the smooth muscle pacemaker interstitial cell of cajal or similar cells they are defined as tumors whose behavior is driven by mutations in the kit gene 85 pdgfra gene 10 or braf kinase rare 95 of gists stain positively for kit cd117. Gastrointestinal stromal tumors gastrointestinal stromal tumors gists start in very early forms of special cells in the wall of the gi tract called the interstitial cells of cajal iccs iccs are sometimes called the pacemakers of the gi tract because they signal the muscles in the gi tract to contract to move food and liquid along. If you have a gastrointestinal stromal tumor gist or are close to someone who does knowing what to expect can help you cope here you can find out all about gastrointestinal stromal tumors including risk factors symptoms how they are found and how they are treated