Imatinib mesylate (Gleevec) has a lasting effect on advanced gastrointestinal stromal tumors (GISTs), while greatly reducing their size, according to the results of a study presented at the 38th annual meeting of the American Society of Clinical Oncology.
"Gleevec has extended the lives of so many cancer patients who would have had no other treatment 5 years ago," said Margaret von Mehren, MD, a medical oncologist at Fox Chase Cancer Center in Philadelphia and a principal investigator for the study. "Most of our GIST patients have been taking Gleevec for at least a year now, and we continue to see encouraging responses."
The study results were derived from updated data of the phase II, multicenter trial in which a daily dose of imatinib(Drug information on imatinib) (either 400 or 600 mg) was given orally to each of the 147 participating patients. At a median follow-up of 15 months, 73% of the patients remain in the study. More than 60% responded well to imatinib, with their tumors decreasing in size by at least one-half. Another 20% had tumors that shrank by one-quarter to one-half, or stabilized.
"In addition to the high rate of overall response to Gleevec, the drug is generally well-tolerated," said Dr. von Mehren. "Not only do we have patients living longer than before with this advanced disease, but most of these patients feel well also."
Some patients experienced mild side effects that included nausea, diarrhea, muscle cramps, and skin rash. About 20% of patients had severe side effects that included low white blood cell counts, tumor hemorrhage, and abdominal pain. To date, researchers have reported no statistically significant difference in response rate between the two dosages.
"For reasons not yet known, the disease progressed in about 18% of patients who initially had tumor shrinkage," said Dr. von Mehren. "For some patients, the growth of disease occurs only in some areas but not in all disease sites. Patients still take Gleevec to control disease. Laboratory studies are already under way at Fox Chase Cancer Center and other institutes to understand why these tumors stopped responding to the Gleevec. More data will need to be collected before determining how many patients this is happening to and why."