P-0123 Outcome of Gist's with Imatinib Mesylate: An Indian Experience.

Abstract

ABSTRACT Introduction GIST represents an uncommon form of malignancy and one of best paradigms of molecularly targeted therapy. While the natural history of GIST following treatment with imatinib mesylate is relatively well known from various series in western literature, rarely any series from developing world has been published in this regard. Methods Forty four GISTs cases diagnosed and treated with imatinib between 2003 and 2009 were retrieved from the Department of Medical Oncology database, KMIO, Bangalore. Their clinical, histopathological data and treatment outcome were analysed. Kaplan Meier survival analysis was done. Anatomic site, tumor size, mitotic activity and extent of resection were correlated with overall survival using the Log Rank test. Results Median age was 56 years (range 21-68 years) with a male : female ratio of 2:1.Stomach (52%) was the most commonly involved site followed by small intestine (36%). Twenty nine cases had disease localized to a single site and 15 cases were metastatic at presentation. Mean tumor size was 10.5 cm (range 4–18cm) and mitotic rate of 6 (range 4-9)/50 HPF. NIH 2002,” Fletchers” criteria was applied for non metastatic disease, none had very low risk, 1 case (3%) had low risk, 10 (34%) intermediate and 18 (65%) belonged to high risk. All cases underwent upfront surgery with R0 resection (84%), R1 (13%) and R2 resection in 3%cases followed by imatinib (400 mg/day) for duration of one year. Metastatic sites in descending frequency of involvement were liver (85%), peritoneum (13%), omentum (6%) and lungs (1%). None had lymph node or soft tissue involvement. In the adjuvant group, median follow-up was 42 months (m) (range 10-70 m).Estimated recurrence free survival (RFS) and overall survival (OS) at 42 m were 59.9 % and 80.6 % respectively. In metastatic group, median follow up was 28 months (range 2-54 m). The median progression free survival (PFS) and OS were 18m [95 %CI 8.65m – 27.34 m] and 28m [95 %CI 17.90 m-38.09 m] respectively. Estimated PFS and OS at 28 months were 38.7% and 46.7% respectively. Non gastric GIST, R2 resection, tumor size (> 10 cm) and mitotic rate>5 (per 50 HPF) were associated with negative impact on survival Conclusion Non gastric GISTs, R1, R2 resection, tumor size (> 10cm) and mitotic rate>5/50 HPF had a negative impact on survival. However, one limitation of our study is the small sample size. This obviates the need for larger prospective studies to determine the optimal duration of adjuvant therapy across various risk groups.