First approved in May 2001 for treatment of chronic myeloid leukemia (CML), imatinib works by blocking enzymes that play a role in cancer growth.
In CML, imatinib blocks the abnormal tyrosine kinase enzyme that plays a major role in that disease.
In GIST, imatinib blocks a different abnormal enzyme found on the tumor cells.
As these abnormal enzymes are largely confined to cancer cells, there is relatively little damage to normal cells, while cancer cells are killed.
In the study that was the basis for imatinib's approval for treatment of GIST, 147 patients with unresectable or metastatic GIST received daily oral imatinib treatment.
While no patient had complete disappearance of cancer, 56 patients (38%) had reduction in tumor size by 50% or greater.
|38% of patients had reduction in tumor size by 50% or greater.
Patients were not followed long enough to determine the duration of the responses.
Imatinib has been approved under accelerated approval regulations and under the orphan drug program, which provides financial incentives for drugs developed to treat rare diseases.
Accelerated approval requires continued patient follow-up and information from additional studies to evaluate whether imatinib provides an actual clinical benefit such as improved survival.
Commonly reported side-effects include edema, nausea, vomiting, diarrhea, skin rash, muscle cramps, liver toxicity, and lower blood cell counts.
Side-effects are generally mild to moderate in severity and rarely require that imatinib doses be decreased or interrupted for prolonged periods of time.
Seven GIST patients had hemorrhage into the tumor or gastrointestinal tract that required red blood cell transfusions.
The drug is manufactured by Novartis AG for Novartis Pharmaceuticals Corporation, East Hanover, New Jersey, USA.