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Oncology & Hematology Review (US) Highlights Gastrointestinal Stromal Tumors (GIST)—Paving the Way for Modern Oncology—Epidemiology, Diagnosis, Treatment Elena Tsvetkova, MD, FRCPC, 1 E Celia Marginean, MD, FRCPC, FACP, 2 with Carolyn Nessim, MD, MSc, FRCSC 3 and Shailendra Verma, MD, FRCPC, FACP 4 1. Medical Oncologist, Department of Medical Oncology, The Ottawa Hospital Cancer Centre, Ottawa, Ontario, Canada 2. Associate Professor of Pathology, Department of Pathology and Laboratory Medicine, Faculty of Medicine, University of Ottawa, Ontario, Canada; 3. Surgical Oncologist and Assistant Professor of Surgery, University of Ottawa; Clinician Investigator, Ottawa Hospital Research Institute, Ottawa General Hospital, Ontario, Canada; 4. Medical Oncologist, The Ottawa Hospital Cancer Centre and Associate Professor, Department of Medicine, University of Ottawa, Ontario, Canada Abstract Gastrointestinal stromal tumors (GIST) are relatively rare tumors arising in the gastrointestinal tract. Clinical presentations of GIST are related to the site of origin, tumor size, and presence of ulceration. Surgery followed by adjuvant treatment with the BCR-ABL tyrosine kinase inhibitor, imatinib, for 3 years, in high-risk tumors is the only curative modality. Neoadjuvant treatment with imatinib may be considered in the setting of locally advanced primary borderline resectable/unresectable disease. Treatment with imatinib in patients with metastatic or unresectable disease is associated with significant improvements in overall survival (OS) from 18 to 57 months. In patients with metastatic disease, those responding to imatinib therapy may be considered for surgery and this may be beneficial if resection of the primary and metastatic disease is feasible and if imatinib is continued post resection. Other locoregional treatments such as radiofrequency ablation (RFA) and hepatic artery embolization (HAE) with or without chemotherapy may achieve long-lasting disease control and may be considered in highly selected patients. In patients with primary or secondary resistance to imatinib, second-line treatment with sunitinib and third-line treatment with regorafenib is recommended. However, despite all of these advances, few patients with metastatic disease are cured and further trials of novel agents or combinations are required. Keywords Gastrointestinal stromal tumor, GIST, imatinib, adjuvant, resection, locoregional treatment, metastatic, management, diagnosis, presentation, neoadjuvant Disclosure: Elena Tsvetkova, MD, FRCPC, E Celia Marginean, MD, FRCPC, FACP, Carolyn Nessim, MD, MSc, FRCSC, and Shailendra Verma, MD, FRCPC, FACP, have no conflicts of interest to declare. No funding was received in the publication of this article. Acknowledgments: All authors have contributed equally to this manuscript. Open Access: This article is published under the Creative Commons Attribution Noncommercial License, which permits any noncommercial use, distribution, adaptation, and reproduction provided the original author(s) and source are given appropriate credit. Received: March 31, 2015 Accepted: April 21, 2015 Citation: Oncology & Hematology Review, 2015;11(1):74–86 Correspondence: Shailendra Verma, MD, FRCPC, FACP, Box 500, The Ottawa Hospital Cancer Centre, 501 Smyth Road, Ottawa, ON K1H 8L6, Canada. E: Gastrointestinal stromal tumors (GIST) are the most common mesenchymal tumors of the gastrointestinal (GI) tract. Although they have been recognized as a distinct entity for several decades, it has only been over the past 10–15 years that these tumors have been truly studied and further defined by rigorous diagnostic and molecular criteria. Indeed, one might argue that it was a landmark study involving the successful treatment of unresectable GIST that launched a new era of targeted therapy in clinical oncology. In the ensuing years we have further refined our knowledge of GIST, developed rigorous diagnostic techniques, surgical interventions and prognostic criteria. Considerable strides have also been made in adjuvant therapy of successfully resected localized tumors and in the setting of widespread disease. In this article, we review the recent progress that has been made in all of these domains. Tou ch MEd ica l MEdia Section 1—Epidemiology—Clinical and Pathologic Considerations Elena Tsvetkova, E Celia Marginean, and Shailendra Verma Epidemiology In the past, the diagnosis of GIST has been fraught with difficulty and they have often been misdiagnosed as leiomyoma, leiomysarcoma, neurofibroma, or benign/borderline malignant potential tumors. Consequently, information on the true incidence or prevalence is scarce and has been largely dependent on retrospective or population- based studies. The identification of the specific expression of the KIT protein (CD117) as a reliable phenotypic marker of GIST has led to a re- appraisal and re-evaluation of pathologic diagnosis and has provided more concrete information. International epidemiologic data derived from Sweden and The Netherlands suggests an annual incidence of 14.5 and approximately 12.3 per million, respectively. 1,2 A population- based study by Tran et al., 3 utilizing the Surveillance, Epidemiology and 57