May 21 (HealthDay News) -- Researchers are reporting that they've discovered a way to boost chemotherapy and slightly extend the lives of mice with pancreatic cancer, potentially paving the way for more effective treatments in people.

There's no guarantee that the strategy would work in humans. And, even if it did, the researchers don't expect that it would add many months to people's lives.

Still, scientists are "cautiously optimistic," said Dr. David Tuveson, lead author of a study released online May 21 in Science and a researcher at the Cambridge Research Institute in England.

Questions about such factors as cost, though, remain to be answered, Tuveson acknowledged.

Pancreatic tumors are among the most difficult types of cancer to treat. Roughly 5 percent of people diagnosed with the more common form of the disease are expected to survive five years from diagnosis, according to the American Cancer Society.

"It usually gets diagnosed when it is already very advanced because the symptoms don't usually begin until the cancer is advanced," said Dr. Allyson J. Ocean, assistant professor of medicine at the Jay Monahan Center for Gastrointestinal Health at New York-Presbyterian Hospital/Weill Cornell Medical College in New York City. Pancreatic cancer is resistant to chemotherapy and radiation, she added, and tumors are often aggressive and likely to spread.

Doctors think the disease is especially difficult to treat with chemotherapy because the tumors don't have many blood vessels to carry drugs to where they need to be to kill cancer cells.

In the study, researchers genetically engineered mice to develop a form of pancreatic cancer. The scientists then gave them a chemotherapy drug called gemcitabine (Gemzar) and another compound they hoped would boost blood flow in the tumors.

The survival time of the mice, on average, doubled from 11 to 25 days when they were treated with the chemotherapy drug and the compound, which is known only by a code. That may not seem like much, Tuveson said, but in people, "a doubling of overall survival from six to 12 months would be meaningful."

Dr. Aaron Sasson, chief of gastrointestinal surgical oncology at the University of Nebraska Medical Center, pointed out that some previous pancreatic treatments have worked well in mice but failed in humans. But the researchers behind the new study may have discovered a "trick" to a more effective treatment, he said.

Nonetheless, it would be quite some time before the treatment could reach doctors' offices, he said. Cost could be an issue, too: Some chemotherapy drugs, he said, cost thousands of dollars a month.

In the big picture, the treatment might extend life span by just a few months, he said. But the strategy could help make tumors more vulnerable to other types of chemotherapy drugs.

"It's possible that other chemotherapy drugs that failed before could become effective," he said.

SOURCES: David Tuveson, M.D., researcher, Cambridge Research Institute, Cambridge, England; Aaron Sasson, M.D., associate professor, surgery, and chief, gastrointestinal surgical oncology, University of Nebraska Medical Center, Omaha; Allyson J. Ocean, M.D., assistant professor, medicine, Jay Monahan Center for Gastrointestinal Health, New York-Presbyterian Hospital/Weill Cornell Medical College, New York City; May 21, 2009, Science