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Chapter 087. Gastrointestinal Tract Cancer (Part 6)

Gastric (Nonlymphoid) Sarcoma Leiomyosarcomas and GISTs make up 1–3% of gastric neoplasms. They most frequently involve the anterior and posterior walls of the gastric fundus and often ulcerate and bleed. Even those lesions that appear benign on histologic examination may behave in a malignant fashion. These tumors rarely invade adjacent viscera and characteristically do not metastasize to lymph nodes, but they may spread to the liver and lungs. The treatment of choice is surgical resection. Combination chemotherapy should be reserved for patients with metastatic disease. All such tumors should be analyzed for a mutation in the c-kit receptor. GISTs. | Chapter 087. Gastrointestinal Tract Cancer Part 6 Gastric Nonlymphoid Sarcoma Leiomyosarcomas and GISTs make up 1-3 of gastric neoplasms. They most frequently involve the anterior and posterior walls of the gastric fundus and often ulcerate and bleed. Even those lesions that appear benign on histologic examination may behave in a malignant fashion. These tumors rarely invade adjacent viscera and characteristically do not metastasize to lymph nodes but they may spread to the liver and lungs. The treatment of choice is surgical resection. Combination chemotherapy should be reserved for patients with metastatic disease. All such tumors should be analyzed for a mutation in the c-kit receptor. GISTs are unresponsive to conventional chemotherapy 50 of patients experience objective response and prolonged survival when treated with imatinib mesylate Gleevec 400-800 mg PO daily a selective inhibitor of the c-kit tyrosine kinase. Many patients with GIST whose tumors have become refractory to imatinib subsequently benefit from sunitinib Sutent another inhibitor of the c-kit tyrosine kinase. Colorectal Cancer Incidence Cancer of the large bowel is second only to lung cancer as a cause of cancer death in the United States 153 760 new cases occurred in 2007 and 52 180 deaths were due to colorectal cancer. The incidence rate has remained relatively unchanged during the past 30 years while the mortality rate has decreased particularly in females. Colorectal cancer generally occurs in persons 50 years. Polyps and Molecular Pathogenesis Most colorectal cancers regardless of etiology arise from adenomatous polyps. A polyp is a grossly visible protrusion from the mucosal surface and may be classified pathologically as a nonneoplastic hamartoma juvenile polyp a hyperplastic mucosal proliferation hyperplastic polyp or an adenomatous polyp. Only adenomas are clearly premalignant and only a minority of such lesions becomes cancer. Adenomatous polyps may be found in the colons of 30 of .