Gastrointestinal Stromal Tumors Respond to Tyrosine Kinase-targeted Therapy

Gastrointestinal stromal tumors (GISTs) are rare tumors of the wall of the stomach and small bowel, and also occasionally arise in the mesentery, omentum, or retroperitoneum. The incidence of GIST in the United States is approximately 500 to 750 patients per 100,000 people. GISTs often present late in their clinical course unless they are the cause of gastrointestinal bleeding or perforation. Surgical resection is the standard of care for primary GIST. However, there is a high risk of recurrence in the peritoneum and liver. For metastatic GIST, imatinib mesylate is the standard of care. Two phase III studies presented in 2003 in abstract form show slightly different results. In the US study, 400 mg/d was found to be equivalent to 800 mg/d with respect to response, progression-free survival, and overall survival at 12 months. In the European/Australasian study, the response rate was the same with either dosage, but progression-free survival was better with 800 mg/d compared with 400 mg/d. Overall survival data for the latter study were too immature for analysis as of May 2003. Adjuvant or neoadjuvant therapy with imatinib is the topic of at least three studies through the American College of Surgeons Oncology Group and Radiation Therapy Oncology Group and the American College of Radiology Imaging Network. Every effort to enroll eligible patients on these studies should be made. New treatments for metastatic disease under investigation include a tyrosine kinase inhibitor with an expanded panel of targets compared with imatinib (SU011248), and the addition of a mammalian target of rapamycin (mTOR) inhibitor and the rapamycin derivative RAD001 to imatinib. Given the finding of a specific molecular defect to exploit, GISTs have gone from an orphan disease to a proving ground for tyrosine kinase-targeted therapy.