Pfizer Inc.‘s experimental drug Sutent improved survival and reduced tumor growth in patients with a type of stomach cancer, according to a pivotal-stage trial the company unveiled this weekend.

The study, the final one before the company seeks U.S. Food and Drug Administration approval for the drug, involved 300 patients with gastrointestinal Stromal tumors whose cancer had become resistant to Gleevec (or Glivec), a drug sold by Novartis AG.

Results, presented here at a meeting of the American Society of Clinical Oncology, showed Sutent prolonged the time it took before tumors grew to 6.3 months from 1.5 months and improved survival by about 50 percent, compared to placebo.

The world’s biggest drugmaker said it planned to file for FDA review of the drug as a treatment for gastrointestinal Stromal tumors before the end of the year.

The trial was stopped ahead of schedule in January after investigators said patients on placebo should be switched to Sutent, given the drug’s demonstrated activity.

Sutent is designed to block biological switches involved in the growth of tumors and the blood vessels that support them.

Dr. William Slichenmyer, vice president of oncology drug development at Pfizer, said the company chose to first study the drug in the stomach cancer indication because patients have no other alternatives once they have stopped responding to Gleevec.

“This represents an extremely hopeful outcome for cancer patients ... by inhibiting these abnormal signals with new rationally designed drugs, we can offer patients the benefits of disease control and longer survival,” the study’s lead author Dr. George Demetri of Dana-Farber Cancer Institute in Boston, said in a statement.

About 75 percent to 80 percent of patients on Gleevec eventually become resistant to the drug, said Dr. Michael Heinrich, professor of medicine, hematology and medical oncology at Oregon Health and Science University in Portland.

“The big news is that this is an unmet medical need. Now there is at least one drug that appears to offer hope,” he said. “We are starting to show a way in oncology to target cancer cells in different ways.”

Still, Pfizer faces competition and its drug has an array of side effects that could limit its use in some patients. For one thing, it causes fatigue to the point that patients must take a two-week break after each four-week period of treatment to recover, the company said.

Sutent can also cause white blood cell counts to fall, making patients more susceptible to infection, and it can cause nausea and diarrhea.

Novartis is racing to develop a drug of its own - AMN107 - to treat patients who become resistant to Gleevec. A late-stage trial of the drug in patients with Gleevec-resistant leukemia-like disorders began recently.

David Epstein, Novartis’s head of oncology, said in an interview this weekend that a separate trial of AMN107 in gastrointestinal Stromal tumor patients will begin later this year.

The drug negates almost all of the known mutations that cause people to become resistant to Gleevec, meaning it could be highly effective with a potentially more favorable safety profile, Epstein said.

Pfizer also presented promising earlier-stage for Sutent in kidney cancer and is slated to present results from trials in breast cancer and neuroendocrine tumors.

On Saturday, 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.

The company expects to have results late next year from a late-stage trial comparing Sutent to interferon as a first-line treatment for kidney cancer.