A PET scan shows the brain on the left has little or no amyloid plaques, which are a hallmark for Alzheimer’s. The brain on the right is positive for amyloid, which is shown as red and yellow in the image. (Alzheimer’s Association/IDEAS-Study)

A major study announced Wednesday gives significant weight to the hypothesis that targeting amyloid plaques in the brain could hold the key to fighting Alzheimer’s disease, offering fresh hope in the battle against a devastating illness that has been impossible to cure.

The study, presented at the Alzheimer’s Association International Conference in Chicago, found that BAN2401, an anti-amyloid antibody, was successful in slowing the progression of the disease and reducing the amount of amyloid accumulated in the brain in 856 patients with early Alzheimer’s.

The treatment was administered at different dosing levels. After 18 months, those receiving the highest dose had an 81 percent reduction in amyloid buildup as measured in PET scans and a 30 percent reduction in clinical indicators of early Alzheimer’s.

“This is the first late-stage anti-amyloid antibody study to successfully achieve statistically significant results at 18 months, further validating the amyloid hypothesis,” said Lynn Kramer, chief clinical officer and chief medical officer with the Neurology Business Group at Eisai, which developed the drug along with Biogen. Kramer said the companies would work on making the drug available to patients as soon as possible.

An estimated 5.7 million Americans 65 and over have Alzheimer’s, and the Alzheimer’s Association predicts that number to mushroom to nearly 14 million by 2050 in the absence of new treatments. A handful of drugs approved by the Food and Drug Administration can alleviate some symptoms, but in the past 14 years no new drugs have been approved for the disease.

The results of the BAN2401 study are similar to promising results two years ago from a trial of another antibody, known as aducanumab, that targets amyloid. That drug also seemed to work best in higher doses. Like aducanumab, BAN2401 caused minor brain swelling among some patients — in this case, 10 percent of them. But this trial was much larger.

James Hendrix, director of global science initiatives at the Alzheimer’s Association, hailed the results, noting that improved cognitive outcomes in patients whose PET scans showed reduced amyloid were a strong indicator in favor of the amyloid hypothesis.

“I think it’s a big deal, because we’ve definitely had some disappointments in Alzheimer’s drug development lately, so I think we just need some positive news,” he said. “We’re obviously very hopeful.”

Alfred Sandrock, executive vice president and chief medical officer at Biogen, called the breakthrough “both exciting and humbling.”

The companies said they hope to pursue further trials and plan to seek regulatory approvals for the treatment.