Targeted Therapy for Imatinib-Resistant GI Cancer Approved
On January 26, the Food and Drug Administration (FDA) approved the experimental drug sunitinib (Sutent) for treating an uncommon gastrointestinal cancer in patients who are resistant to or unable to take the primary treatment, imatinib (Gleevec).
Many patients with this cancer, gastrointestinal stromal tumor (GIST), become resistant to imatinib within 2 years.
Sunitinib is a targeted therapy that inhibits multiple proteins involved in the growth of cancer cells and the formation of blood vessels that supply tumors with nutrients, a process called angiogenesis.
The drug was also approved for treating advanced renal cell carcinoma, a form of kidney cancer.
In granting approval for GIST, the FDA cited results from a randomized phase III clinical trial comparing sunitinib and placebo in more than 300 patients who had failed imatinib therapy.
The findings had been presented earlier that day at the 2006 Gastrointestinal Cancers Symposium in San Francisco.
The results show that the relative risk of death was reduced by half in the sunitinib group compared with the placebo group, and the time for cancers to progress was more than four times longer in the sunitinib group than in the placebo group.
Median overall survival has not yet been reached in this ongoing research study. The independent committee monitoring data during the trial made sunitinib available to all participants after interim results clearly favored the drug.
A small group of patients who could not take imatinib took sunitinib as a first-line treatment and had "excellent" responses, the researchers said. The drug, a capsule taken once daily, was generally well tolerated by patients.
Sunitinib, which was previously referred to by the code name SU11248, will be marketed by Pfizer. The drug is the first targeted therapy proven to be effective in a randomized trial after another targeted therapy failed, but others are being evaluated.
"We expect to see a lot more of these targeted therapies appearing in rapid succession," said Dr. George Demetri of the Dana-Farber Cancer Institute, who presented the findings in San Francisco.
He calls sunitinib a "multitargeted" therapy because in addition to blocking the KIT and PDGFRA proteins, which are targeted by imatinib, the new drug also inhibits multiple signaling proteins involved in angiogenesis and tumor growth.
To illustrate the drug's effectiveness, Dr. Demetri described a GIST patient who began taking sunitinib after imatinib failed. The patient's pain was relieved and the tumor stopped growing within a week, but it took 8 months of therapy for the tumor to shrink.
"The drug was shutting down the disease, but it did not shrink the tumor initially," Dr. Demetri said. Targeted therapies, he suggested, may increasingly help patients live longer "by controlling the disease even if they do not change the size of tumors."
The effects of these new therapies on tumors, he adds, can be seen with imaging technologies that are now used to develop targeted agents.
The development of sunitinib has been rapid. The drug was first taken by a patient with GIST in 2002 - just 4 years before FDA approval was announced.
By Edward R. Winstead