Adjuvant imatinib for 3 years better than 1 year in high-risk GIST



After surgery for high-risk gastrointestinal stromal tumor (GIST), patients who received adjuvant imatinib for 3 years achieved longer relapse-free survival (RFS) and overall survival (OS) compared with those treated for 1 year, according to a study published online in Journal of Clinical Oncology.

With a median follow up of 7.5 years, the 5-year survival rates of greater than 90% represent the highest reported to date in high-risk GIST.

“We speculate that, other than adjuvant imatinib, two procedures were crucially important for achieving the high overall survival rates: longitudinal monitoring of the abdomen with CT to detect GIST recurrence early when the tumor bulk was still small and restarting of imatinib after recurrence was detected,” wrote Dr. Heikki Joensuu of the Comprehensive Cancer Center Helsinki and University of Helsinki, Finland, and colleagues.

Five-year RFS rates for 3- and 1-year treatment durations were 71.1% and 52.3%, respectively (hazard ratio, 0.60; 95% CI, 0.44-0.81; P less than .001); 5-year OS rates were 91.9% and 85.3%, respectively (HR, 0.60; 95% CI, 0.37-0.97; P = .036), the investigators reported (J Clin Oncol. 2015 Nov. 2. doi: 10.1200/JCO.2015.62.9170).

After a median follow up of 90 months, the second planned analysis of the open-label Scandinavian Sarcoma Group XVIII/AIO study evaluated outcomes of 358 patients, 181 in the 12-month group and 177 in the 36-month group. Earlier results from the SSGXVIII/AIO trial (after a 4.5-year follow up) showed significantly longer survival in patients who received imatinib for 3 years versus 1 year, and these results have informed treatment guidelines.

However, two other large randomized trials evaluated adjuvant imatinib for durations less than 3 years in patients with lower-risk GIST, and neither study found a survival benefit. The investigators point out that because low- or intermediate-risk GIST is cured with surgery alone in the great majority of patients, most do not benefit from adjuvant imatinib.

“Hypothetically, these results suggest that obtaining overall survival benefit may require durable administrations of imatinib and that the patients at high risk for recurrence are the optimal target population,” they wrote.

All but two patients reported at least one adverse event, but most events were mild. Previous reports have suggested cardiac toxicity of imatinib, but only one patient had cardiac failure, perhaps due to the low 400 mg adjuvant daily dosage.

Dr. Joensuu reported consulting or advisory roles with Blueprint Medicines, ARIAD Pharmaceuticals, and Orion Pharma. Several of his coauthors reported ties to industry sources.

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