Biogen Inc. shares surged by more than 32% after documents prepared for a Food and Drug Administration advisory panel concerning the company’s experimental Alzheimer’s drug were released.

The effect of the drug is “robust and exceptionally persuasive” in one study, FDA staff said Wednesday. Agency drug reviewers wrote that an examination of a second study on the drug, called aducanumab, that hadn’t shown favorable results didn’t represent evidence it was not effective.

The findings were posted ahead of a Friday meeting where outside advisers to the FDA will hear from agency staff and Biogen about the drug’s safety and effectiveness. The committee will then make nonbinding recommendations to the FDA as its leadership weighs approval.

About 5.8 million Americans are living with Alzheimer’s dementia, according to the Alzheimer’s Association. Other approved drugs temporarily improve some symptoms, but none slow or stop the destruction of neurons in the brain that cause the symptoms and make the disease fatal, the association said in a report last year.

If aducanumab reaches the U.S. market, sales are expected to total about $4.7 billion in 2025, according to data compiled by Bloomberg. Biogen developed the therapy with partner Eisai Co., a pharmaceutical company based in Japan.

Biogen halted clinical trials on the drug in March 2019 after determining that aducanumab was unlikely to work, but then reversed course in October after reviewing more data and declared that one of the two trials had been successful.

The Cambridge, Massachusetts-based company presented data from two trials at a conference in December. One trial showed the drug may slow the progression of the disease, while the other found no effect. Researchers questioned the positive results because not all participants completed the trial before it was stopped.

Aducanumab targets amyloid plaque that builds up in the brains of Alzheimer’s patients. Brain scans showed the drug removed the plaque, but whether that had any benefit is unclear. While the plaque is found in the brains of Alzheimer’s patients, scientists don’t know what role it plays in the disease.

More than 40% of patients who took high doses of aducanumab developed brain swelling or hemorrhages. Most didn’t develop symptoms but the side effects were seen on brain scans.