Gastrointestinal Stromal Tumor (GIST)

Gastrointestinal stromal tumors (GISTs) are the most common sarcoma of the GI tract and account for 1–3 % of all GI malignancies. GISTs arise from the interstitial cells of Cajal, an intestinal pacemaker cell located in and around the myenteric plexus. They typically arise in the stomach (65–70 %) or small intestine (25–45 %). An important immunohistochemical marker is KIT, a membrane receptor with tyrosine kinase activity that is present in most GISTs (80–95 %). Some GISTs (5–7 %) have a mutation in platelet-derived growth factor receptor alpha (PDGFRA) instead. Several factors including tumor site, size greater than 5 cm, and greater than 5 mitoses per 50 high-power field predict aggressive behavior and recurrence. The treatment for localized GISTs is resection. Systemic chemotherapy and radiation are ineffective. The tyrosine kinase inhibitor imatinib improves progression-free survival in patients with metastatic disease, and its use in the adjuvant and neoadjuvant settings is increasingly common. Many patients ultimately develop imatinib resistance, and for these patients, dose escalation or the use of another tyrosine kinase inhibitor is recommended.