A team of researchers inside Pfizer made a startling find in 2015: The company’s blockbuster rheumatoid arthritis therapy Enbrel, a powerful anti-inflammatory drug, appeared to reduce the risk of Alzheimer’s disease by 64 percent.

The results were from an analysis of hundreds of thousands of insurance claims. Verifying that the drug would actually have that effect in people would require a costly clinical trial — and after several years of internal discussion, Pfizer opted against further investigation and chose not to make the data public, the company confirmed.

Researchers in the company’s division of inflammation and immunology urged Pfizer to conduct a clinical trial on thousands of patients, which they estimated would cost $80 million, to see if the signal contained in the data was real, according to an internal company document obtained by The Washington Post.

“Enbrel could potentially safely prevent, treat and slow progression of Alzheimer’s disease,’’ said the document, a PowerPoint slide show that was prepared for review by an internal Pfizer committee in February 2018.

Drug companies frequently have been pilloried for not fully disclosing negative side effects of their drugs. What happens when the opposite is the case? What obligation does a company have to spread potentially beneficial information about a drug, especially when the benefits in question could improve the outlook for treating Alzheimer’s, a disease that afflicts at least 500,000 new patients per year?

A medical ethics expert argued that Pfizer has a responsibility to publicize positive findings, although it is not as strong as an imperative to disclose negative findings.

“Having acquired the knowledge, refusing to disclose it to those who might act upon it hides a potential benefit, and thereby wrongs and probably harms those at risk of developing Alzheimer’s by impeding research,’’ said Bobbie Farsides, professor of clinical and biomedical ethics at Brighton and Sussex Medical School in the United Kingdom.

Meanwhile, Enbrel has reached the end of its patent life. Profits are dwindling as generic competition emerges, diminishing financial incentives for further research into Enbrel and other drugs in its class.

“I’m frustrated myself really by the whole thing,’’ said Clive Holmes, a professor of biological psychiatry at the University of Southampton in Great Britain­­ who has received past support from Pfizer for Enbrel research in Alzheimer’s, a separate 2015 trial in 41 patients that proved inconclusive.

He said Pfizer and other companies do not want to invest heavily in further research only to have their markets undermined by generic competition.

“Someone can pop up and say, ‘Look, I’ve got a me-too drug here,’ ’’ Holmes said, referring to the advent of generic versions of Enbrel. “I think that is what this is all about.’’

Enbrel reduces inflammation by targeting a specific protein called TNF-a. The Pfizer claims data analysis added to a growing body of evidence that broadly targeting TNF-a in the body has the potential to prevent Alzheimer’s, said Holmes, the professor of biological psychiatry at the University of Southampton.

Holmes is among the few researchers who has gained access to the Pfizer data; he won the company’s permission to use it in a grant application for a small clinical trial he is undertaking in England.

“If it’s true in reality, if you did it in a clinical trial setting, it’s massive — it would be huge,’’ Holmes said. “That’s why it’s so exciting.’’

Pfizer said it also was skeptical because Enbrel has only a limited effect on the brain. The Enbrel molecule is too large to pass through the “blood-brain barrier’’ and directly target TNF-a in brain tissue, the company said.

Yet Alzheimer’s researchers believe inflammation outside the brain — called peripheral inflammation — influences inflammation within the brain.

“There is a lot of evidence suggesting that peripheral or systemic inflammation may be a driver of Alzheimer’s disease,’’ said Walker, the Johns Hopkins researcher. It is a fair hypothesis that fighting inflammation outside the brain with Enbrel will have a similar effect inside the brain, he said.

“I don’t believe Enbrel would need to cross the blood brain barrier to modulate the inflammatory/immune response within the brain,’’ Walker said.

“There is increasing evidence that peripheral inflammation can influence brain function,’’ said rheumatologist Christopher Edwards, of the University of Southampton in Britain.

“It’s important that that’s published, and in the public domain,’’ Edward added of the Pfizer data. “It needs to be out there.’’

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