For the first time, researchers are reporting that a treatment might help stabilize Alzheimer’s disease for as much as three years, although the evidence is weak.

The drug is Gammagard, made by Baxter International Inc. Doctors say that four patients who have been receiving the highest dose for three years showed no decline on memory and cognition tests. A dozen others on different doses or shorter treatment times didn’t fare as well. This study was too small to prove the treatment works, but a more rigorous one involving 400 patients will give results within a year.

Still, the findings from the small study encouraged doctors at the Alzheimer’s Association International Conference in Vancouver, British Columbia, where they were presented on Tuesday.

“It’s tantalizing. If you were to pick out four people with Alzheimer’s disease, the likelihood that they would perform the same on standardized tests three years later is very, very tiny,” said William Thies, the association’s scientific director.

People typically go from diagnosis to death in about eight years, so to be stable for three years “is a long time,” he said. “We shouldn’t get euphoric and we shouldn’t get unreasonable enthusiasm, but this is a positive piece of data.”

In the U.S., about 5 million have Alzheimer’s. Current medicines just temporarily ease symptoms. There is no known cure.

Gammagard is intravenous immune globulin, or IVIG — multiple, natural antibodies culled from donated blood. Half a dozen companies already sell IVIG to treat immune system and blood disorders. These antibodies may help remove amyloid, the sticky plaque that clogs patients’ brains, sapping memory and ability to think.

On Tuesday, Dr. Norman Relkin, head of a memory disorders program at New York-Presbyterian Hospital/Weill Cornell Medical Center, gave three-year follow-up results on 16 of 24 patients in an earlier study of Gammagard aimed at finding the right dose to use in the larger study. The other eight are no longer being followed, and at least some of them have died.