Gleevec"s effects are lasting, researchers believe

Study results revealed May 19 at annual ASCO meeting in Florida

Most gastrointestinal stromal tumor patients who receive Gleevec have a lasting response to the drug and experience significant tumor shrinkage, a new study shows.

The results of the study were presented May 19 at the 38th annual meeting of the American Society of Clinical Oncology. More than 23,000 cancer care professionals from around the world attended this year's meeting in Orlando, Florida, U.S.

One year after beginning treatment with Gleevec, (called Glivec, or imatinib outside the U.S.), 63 percent saw their tumors shrink in half or more, and 20 percent had “stable” disease, meaning their tumors were unchanged or decreased by half or less.

“These responses are lasting and are in marked contrast to standard chemotherapy, which has a response rate of 5 percent," said Dr. Margaret von Mehren, associate member of the Fox Chase Cancer Center in Philadelphia.

“GISTs are an extremely difficult cancer to treat, so the fact that a convenient, oral, once daily therapy, like Gleevec, can offer this type of response is very welcome news to patients and oncologists.”

In this phase II study, 147 patients received Gleevec, either 400 mg or 600 mg a day. The response rate did not differ substantially between the two dosages.

Only 12 percent of patients saw their disease get worse. Studies are already underway to learn why a tumor that initially responded to Gleevec has become resistant to the drug, said von Mehren.

The drug was generally well tolerated, although some patients experienced side effects that included nausea, diarrhea, muscle cramps, and skin rash. About 23 percent of patients had severe side effects that included low white blood cell counts, tumor hemorrhage, and abdominal pain. The drug was discontinued due to “adverse events” in 13 patients (9 percent). Seven patients (5 percent) had gastrointestinal and/or intratumoral bleeding.

Historically, GISTs have been very difficult to treat due to their high levels of resistance to treatment with traditional chemotherapy and radiation.