The U.S. Food and Drug Administration is evaluating clinical data that may suggest Novartis AG's Parkinson's disease treatment Stalevo is linked to an increased risk of prostate cancer.

Data from a long-term clinical trial, known as STRIDE-PD, unexpectedly found that a greater number of patients taking Stalevo had prostate cancer compared to those taking another Parkinson's treatment, the FDA said.

The agency said it has not concluded that Stalevo increases the risk of developing prostate cancer, and advised patients not to stop treatment unless told to do so by their doctors.

"The agency is exploring additional ways to better understand if Stalevo actually increases the risk of prostate cancer," the FDA said in a safety communication posted on its website on Wednesday.

Novartis did not have an immediate comment.

Stalevo — which contains the active ingredients carbidopa, levodopa and entacapone — is marketed in the United States by Swiss-based Novartis and manufactured by Finnish drugmaker Orion.

Novartis reported global sales last year of $554 million for Stalevo and another Parkinson's drug, Comtan, which contains entacapone.

Novartis shares rose 1 percent to $54.19 on the New York Stock Exchange late Wednesday afternoon.