The results showed Sutent lengthened the time it took before tumors grew from 1.5 months to 6.3 months and improved survival by about 50 percent, compared to patients taking a placebo. Pfizer’s drug does have serious side effects that could limit its use. It causes fatigue so severe that patients must take a two-week break after each four-week period of treatment to recover. Sutent can cause white blood cell counts to drop, increasing patients’ vulnerability to infection, and it can also cause nausea and diarrhea. The study is the last to be conducted before the company seeks U.S. Food and Drug Administration approval for the drug, and involved 300 patients with gastrointestinal stromal tumors whose cancer had become resistant to Gleevec, a drug manufactured by Novartis AG. About 75 percent to 80 percent of patients on Gleevec eventually become resistant to the drug.

Sutent may also be effective in treating early-stage kidney cancer, breast cancer and neuroendocrine tumors, according to preliminary results of other trials. Investigators from Memorial Sloan-Kettering Cancer Center in New York said mid-stage trials of Sutent showed that 40 percent of 169 patients with advanced cancer saw their tumors shrink.