The US Food and Drug Administration (FDA) on Thursday approved a new "targeted" drug called sunitinib (Sutent) for use against two types of cancer: gastrointestinal stromal tumor (GIST), a rare form of stomach cancer, and advanced kidney cancer.

The approval covers the use of sunitinib for GIST patients whose disease has progressed or who are unable to tolerate treatment with Gleevec, the current standard therapy. Like Gleevec, sunitinib is a targeted therapy that attacks only certain parts of cells. Both drugs are tyrosine kinase inhibitors, but the new agent attacks more than one target to deprive tumor cells of the blood and nutrients they need to grow.

In an early look at study data, researchers found that sunitinib delayed the time it takes for tumors or new lesions to grow in patients with GIST, according to the FDA statement. Specifically, the median time-to-tumor progression for patients treated with sunitinib was 27 weeks compared to 6 weeks for patients who received an inactive placebo.

Researchers then moved all patients in the GIST trial into treatment with sunitinib.

"[This] approval is a major step forward in making breakthrough treatments available for patients with rare and difficult to treat forms of cancer" said Steven Galson, MD, in an FDA press release. Galson directs the FDA's Center for Drug Evaluation and Research.

Len Lichtenfeld, deputy chief medical officer for the American Cancer Society, said the new approval is exciting news for patients with few other treatment options.

"This is part of a changing landscape in the care of cancer patients," he said. "We've learned a great deal about how cancer cells work, and we've been able to take that knowledge and apply it to drugs that focus on the internal workings of cancer cells."

Sunitinib went through an "accelerated approval" process for advanced kidney cancer, according to the FDA statement. The agency reports that in studies for renal cell carcinoma, sunitinib shrank the size of some patients' tumors by more than half. The overall response rate ranged from 26% to 37% in patients with advanced kidney cancer whose tumors had progressed after the standard treatment with cytokine-based treatments.

"It's a significant accomplishment," said Robert Motzer, MD, a medical oncologist at Memorial Sloan-Kettering Cancer Center who has been treating kidney cancer patients for 20 years. "Finding new treatments has been a priority."

Advanced kidney cancer is very difficult to treat. Traditional chemotherapy and radiation are not very effective against this disease. Interleukin-2 and interferon (cytokine-based treatments) can shrink the tumors, but only 10%-20% of patients respond to these drugs and they can have severe side effects.

The new drug provides new hope to patients who haven't been helped by existing treatments, Motzer said. "It clearly changes the standard of care for people who've had interleukin-2 or interferon."

Motzer said the drug would soon be tested as a first-line treatment for advanced kidney cancer. Such clinical trials are very important, Lichtenfeld said, because it's the only way to know for sure whether the drug will help people earlier in the course of their disease.

The most commonly reported sunitinib-related side effects from both patient groups included diarrhea, skin discoloration, mouth irritation, weakness, and altered taste. Patients also experienced sores on the hands and feet, fatigue, high blood pressure, bleeding, and swelling. Hypothyroidism was also observed.

About 5,000 cases of GIST are diagnosed each year in the US. For kidney cancer, 36,160 new cases were expected in 2005 and about 12,660 people were expected to die of the disease.

Pfizer, Inc makes sunitinib under the brand-name Sutent and reportedly worked with the FDA to expand access to the promising drug even before government approval, so even patients who were not enrolled in these clinical trials could get the product. Sutent is a pill patients take once a day for 4 weeks, followed by a 2 week break. The drug will be available starting Feb. 3, 2006, according to Pfizer.