Androgen deprivation therapy (ADT), a standard treatment for prostate cancer, may lead to double the rate of of Alzheimer’s disease, according to a just-published Stanford/University of Pennsylvania study using a big-data retrospective approach to clinical research.

"In this study, we did find that men who received hormone therapy had about an 88 percent increased risk of Alzheimer's disease," lead study author, Dr. Kevin Nead of the University of Pennsylvania Perelman School of Medicine, told CBS News.

The study, conducted by scientists at the Stanford University School of Medicine and the University of Pennsylvania Perelman School of Medicine, was published online Dec. 7 in the Journal of Clinical Oncology.

"We wanted to contribute to the discussion regarding the relative risks and benefits of ADT, and no one had yet looked at the association between ADT and Alzheimer's disease," Nead told the UK's Western Daily Press.

The possible connection had been talked about. “There was some chatter in the literature,” said senior author Nigam Shah, associate professor of biomedical informatics research at Stanford. "But no one had formally tried to find out if ADT therapy leads to cognitive defects," Shah said, noting that Nead had spotted various references in the literature.

“This is the kind of question that typically you would need a large clinical trial to answer,” said Shah.

A full-blown clinical trial would have been expensive. “So instead, we’re making secondary use of existing clinical data collected as part of routine medical care — clinical data that’s practically free," he said.

The study looked at 5.5 million patients from two hospitals: Stanford Health Care, in Palo Alto and, through a prior institutional research agreement, 3.7 million patients from Mount Sinai Hospital in New York City. Researchers were able to find 16,888 patients in this group who had non-metastatic prostate cancer. Of these, 2,397 had received ADT.

These patients were found to have about a 1.88 times increased rate of being diagnosed with Alzheimer’s disease in a median follow-up period of 2.7 years vs. those not getting ADT. The subset of men getting ADT for more than a year had a 2.12 higher risk — more than double that of prostate cancer patients not treated with ADT.

"Testosterone has been shown to be important for the health of neurons," Nead said, "and neurons make up the brain and if we are not keeping those neurons healthy it could lead to an increased risk of Alzheimer's."

Despite the increased risk, however, ADT is still the treatment of choice — especially as it is typically given to those with advanced prostate cancer, which makes it uncertain if a boost in Alzheimer's risk is actually linked to the ADT or to the severity of the disease. At this point, Dr. Matt Galsky, director of Genitourinary Medical Oncology at Mount Sinai Hospital, told CBS, "the benefits of continuing treatment far outweigh this theoretical risk based on this retrospective study."

Prostate cancer was the third most common cancer in the U.S. in 2015 with an estimated 220,800 new cases and will reportedly lead to the death of an estimated 27,540 people this year.

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