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Imatinib Achieves Durable Results in GIST Patients, but One in Five Develops Resistance: Presented at ASCO

By Peggy Peck

ORLANDO, FL -- May 20, 2002 -- After 15 months of imatinib mesylate treatment, 73 percent of patients with gastrointestinal stromal tumors (GIST) remained on drug, and the response rate held at about 62 percent, according to researchers.

George D. Demetri, MD, medical director, Center for Sarcoma and Bone Oncology, Dana-Farber Cancer Institute and associate professor, Harvard Medical School, Boston, Massachusetts, presented the findings here on May 19 at the 38^th Annual Meeting of the American Society of Clinical Oncology (ASCO).

"[Imatinib] performed much as we had expected," he said, adding that the drug "is helping us transform this disease into a chronic, manageable disease. ... [Imatinib] is still an absolutely awesome drug".

However, Dr. Demetri and colleagues found that about 20 percent of patients appear to develop resistance over time. "The timing of this resistance is highly variable. It can occur early or late, there is no clear pattern," he said.

The study enrolled 147 patients with unresectable and/or metastatic GIST. Patients were randomized to imatinib 400 mg/day or 600 mg/day. The overall rate of partial response (SWOG criteria) is 54 percent, with no significant differences between dose levels. An additional 28 percent of patients had minor responses or stable disease.

Fourteen percent of patients exhibited disease progression. "At 22 months now of follow-up, median survival has not yet been reached," said co-investigator Margaret von Mehren, MD, of Fox Chase Cancer Center in Philadelphia, Pennsylvania.

Seventeen percent of patients in the 400 mg arm developed resistance and were switched to the 600 mg dose. "Many of these patients did recapture response at the higher dose," she said, but she noted that she did not yet have exact numbers on the "recapture" rate.

The majority of adverse events were mild to moderate, consisting mostly of grade 1 and 2 nausea (54 percent), diarrhea (51 percent), periorbital edema (48 percent), muscle cramps (42.2 percent), fatigue (38.8 percent), headache (30.6 percent), and dermatitis (26 percent).

Severe adverse events (grades 3 and 4) associated with imatinib occurred in 21 percent of patients, with equivalent incidence between dose levels: edema (3 percent), GI or tumor hemorrhage (5 percent), abdominal pain (6 percent), neutropenia (5 percent), and fluid retention (5 percent).

Ten patients died of progressive disease and an additional four patients died of other causes, with no direct relationship to imatinib.

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