Results on 86 patients who took part in the trial were reported to the conference of the American Society of Clinical Oncologists in San Francisco, California, USA.
Last month a single case-study highlighting the drug's potential benefits were reported in the New England Journal of Medicine.
The latest trial shows that tumors shrank by 50% or more in 59% of patients. In another 26% of patients the treatment appeared to stop disease progression.
During the trial PET scans were used to monitor patients daily, enabling physicians to chart the effectiveness of the treatment from the moment it began.
The drug, now marketed as 'Gleevec', was approved last week by the US Food and Drug Administration for the treatment of chronic myelogenous leukemia. It works by blocking tyrosine kinase enzymes. GIST is caused by a defect in one such enzyme known as KIT.
|ST1571 (Gleevec) blocks tyrosine kinase enzymes|
|American Society of Clinical Oncologists|
Researcher Dr George Demetri, of the Dana-Farber Cancer Institute, Boston, Massachusetts, USA, said: "This work is based on an understanding of the genetic mechanisms that characterize this type of cancer.
"Laboratory experiments predicted this medication might work in GIST, and we have been tremendously pleased with the clinical benefits which the majority of patients achieved in this trial."
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