People with advanced gastrointestinal stromal tumors (GIST) who take Gleevec (imatinib) for prolonged periods continue to benefit from the drug, according to a five-year study by Oregon Health & Science University Cancer Institute researchers.
The study was led by Charles Blanke, M.D., leader of the OHSU Cancer Institute Solid Tumors Program, with colleagues at OHSU, Dana-Farber Cancer Institute, the Fox Chase Cancer Center, and the University of Helsinki. The study was presented at the recent 2006 annual meeting of the American Society of Clinical Oncology.
It represents the long-term analysis of a randomized clinical trial begun in 2000. More than half of study participants saw their GIST go into remission on Gleevec. Those promising early results prompted the U.S. Food and Drug Administration to approve Gleevec as a treatment for GIST on Feb. 1, 2002.
The long-term analysis, completed in 2005, continues to demonstrate promising results. Eighty-four percent of the 147 GIST study participants on Gleevec showed clinical improvement during the study period, meaning that their disease stabilized or went into remission. Two of those experienced complete remission. However, some subjects developed resistance to the drug and some experienced a relapse of their cancer.
It typically took 13 weeks before a study participant responded to the drug, and the typical positive response lasted 118 weeks (2.3 years).
"This study shows that the response to Gleevec among GIST patients is durable," Blanke said. "Molecularly targeted therapy helps extend their lives."
The long-term study of GIST is especially significant because GIST is a cancer that has been considered untreatable and incurable, with life expectancy of about a year. People in the Gleevec study survived a median of 4.8 years.
Gleevec is a signal transduction inhibitor that interferes with the enzymes that trigger the spread of tumor cells. It acts on GIST by blocking the growth signal of genetic mutations called c-kit and PDGFRA. Subjects with either of these mutations were more likely to respond to Gleevec than those without the mutations.
Most of the persons in the study for whom Gleevec did not work developed resistance to the drug. Among those who developed resistance, the median time to do so was 84 weeks (1.6 years).
Gleevec was initially developed at the OHSU Cancer Institute by Brian Druker, M.D., in collaboration with scientists at Novartis, as a treatment for patients with chronic myelogenous leukemia. In addition to GIST, it is also being studied as a potential therapy for certain types of blood and skin cancers.