Gene expression signatures and response to imatinib mesylate in gastrointestinal stromal tumor

Radiation Therapy Oncology Group S0132 trial design and patient response to imatinib mesylate. A, patients with primary or recurrent operable GIST were screened for KIT (CD117) expression by IHC for eligibility. Before imatinib mesylate treatment, a CT was done, and biopsies were collected by core needle aspiration. Patients were then treated with an 8- to 12-wk regimen of imatinib mesylate, followed by cytoreductive surgery. A CT was also done once during treatment (~4–6 wk into imatinib mesylate treatment) and immediately before surgery. B. Top, percentage of tumor growth based on CT measurements taken from the longest cross-sectional diameter of the primary GIST or the index metastatic lesion(s) for each Radiation Therapy Oncology Group S0132 patient. Bottom, specific samples (pre, post, or both) used for microarray analysis classified as group A or B based on the percent of tumor shrinkage/growth visualized by CT. Mutational analysis of most patients was done and is denoted by color of column (yellow, KIT exon 11 mutants; red, wild-type GISTs; purple, KIT exon 9 mutants; blue, not enough DNA available for mutational analysis). Group A is defined as ≥25% tumor shrinkage after 8 to 12 wk of imatinib mesylate, and group B contains tumors showing <25% tumor reduction, no change, or evidence of tumor enlargement after 8 to 12 wk of imatinib mesylate.