While most of these side effects lessened after about six weeks of treatment, low blood counts occasionally appeared for the first time two months into treatment. These low blood counts improved after temporarily stopping the drug. Patients in the European trial received varying doses of Gleevec and were given the drug for at least one year, or until the tumors started growing again. While the researchers did not report any complete responses, they did note that several patients' tumors appeared to totally disappear on a special type of scan that measures tumor activity. Approximately 5,000 cases of GIST are diagnosed in the U.S. each year, although scientists noted that the actual number might be higher.
Prognosis tends to be poor, even for early tumors that can be removed by surgery.
Clearly beneficial responses like those in the two GIST trials described here are rarely seen in early clinical trials. In a discussion led by Charles Sawyers, M.D., from the UCLA Jonsson Cancer Center in Los Angeles, the enthusiasm continued. Additionally, the drug, while clearly less toxic and much better than traditional chemotherapy or radiation treatments, still has side effects. The other caveat is that genetic mutations in the tumor appear to predict which tumors will respond to the drug. Current studies in GIST, brain tumors and leukemia are ongoing in the U.S. and around the world.