MONDAY, Feb. 11 (HealthDay News) -- Preliminary research produced promising results for a cancer-fighting drug that piggybacks on a virus similar to the one used in the smallpox vaccine.

Patients with advanced liver cancer who were given higher doses of the drug lived months longer than those who took lower doses, and the researchers said some of them are still alive three years later.

There are many caveats. The drug, known as JX-594, is in the early stages of development, and the evidence is years from being ready to be submitted for approval by U.S. Food and Drug Administration officials. The study is also very small, doesn't compare patients who took the drug to those who didn't, and offers no details about its potential cost.

However, the finding is unusual because it suggests that a drug that enters the body through a virus can improve survival in cancer patients, said study co-author Dr. David Kirn, chief medical officer with Jennerex Biotherapeutics, in San Francisco, which is developing the medication. The average survival "more than doubled" in those who took the larger doses. "It's exciting and important for the field, but there's no question we need to confirm it," he said.

William Phelps, director of preclinical and translational cancer research for the American Cancer Society, called the research "promising" and said it reflects the evolution of cancer research toward developing new ways to treat the disease other than the traditional methods of surgery, chemotherapy and radiation, which aim to remove or kill the cancer.

The new drug, like others that are now in development, tries to stimulate the patient's own immune system to fight the cancer. It works by entering the body through an "engineered vaccine" that's similar to the vaccine that prevents smallpox. (The vaccine in this case, like the smallpox vaccine, doesn't cause disease.)

Instead of multiplying in regular cells, the virus in this case only multiplies in cancer cells, study co-author Kirn explained. "It makes thousands of copies and bursts the cancer cell," he said, and then releases a kind of alert to the immune system that tells it that other cancer cells need to be destroyed.

In the new study, the second of three phases required in medical research, scientists gave doses of medication to 30 patients with severe liver cancer. They received three doses, injected into the blood or into their tumors, over a month.

Those who took a higher dose lived for 14 months on average, compared to seven months for those who took the lower dose. The researchers reported that the drug appeared to have an effect not only on the liver tumors but also in cancer cells that had spread elsewhere in the body.

While the study is "by no means definitive" overall, that's good news, said Dr. Neal Meropol, chair of the division of hematology and oncology at Case Western University and the Seidman Cancer Center at University Hospitals, in Cleveland.

As for side effects, patients all felt like they had the flu for about a day, Kirn said. About one-third of those who took the higher dose developed anorexia.

Kirn said the research will continue. He declined to provide a specific estimate of how much the drug will cost, but he did say that its production is not "exceedingly expensive."

The study appears online in the Feb. 10 issue of the journal Nature Medicine.

More information

For more about cancer, visit the U.S. National Library of Medicine.