(CBS) — Shares of Biogen and Japan’s Eisai rallied on Friday, a day after the companies announced that a much-anticipated, experimental Alzheimer’s drug had yielded positive results in a large clinical trial.

It’s a hopeful development in what’s been an uphill battle in treating a disease that has perplexed the medical field for decades.

Patients who received the highest dosage of the experimental drug, BAN2401, showed slower progression of the disease, the drug developers said in a statement.

The advance followed 18 months of treatment, and comes after disappointing results in an earlier analysis after one year.

The brain disease has a devastating impact, taking emotional and financial tolls.

Alzheimer’s, along with other types of dementia, afflicts an estimated 5.7 million Americans.

Unless interventions are found, the Alzheimer’s Association expects the cost of care to hit $1.1 trillion by 2050 in today’s dollars, versus an estimated $277 billion this year.



“The prospect of being able to offer meaningful disease-modifying therapies to individuals suffering from this terrible disease is both exciting and humbling,” Biogen’s chief medical officer, Alfred Sandrock, said in the release.

Eisai said it would discuss next steps with regulators, as another large trial would typically be required to validate the findings.

Shares of the Japanese company surged 19 percent, their daily limit, in Tokyo, while Biogen shares were up 18 percent in late-morning trading in New York on Friday.

Expectations for the study involving more than 800 patients were held in check after a December review failed to achieve its targets.

BAN2401 goes after what could be the most harsh version of a protein called beta amyloid, believed to be involved in the disease as its deposits start forming in the brain years ahead of symptoms emerging.