Evidence backs melanoma-Parkinson's association

NEW YORK (Reuters Health) - People with Parkinson's disease are twice as likely as those without the neurological disorder to get a diagnosis of the skin cancer melanoma, a new review of the evidence concludes.

"It's prudent for Parkinson's patients to be more cautious about their skin health," said Dr. Honglei Chen, the lead author of the study and an investigator at the National Institute for Environmental Health Sciences.

The researchers say the underlying cause of this increased risk for melanoma, the deadliest of the skin cancers, is unknown.

"I think because melanoma and Parkinson's are fairly rare, there's no reason to be alarmed," Chen told Reuters Health.

According to estimates from the National Cancer Institute, each year about 68,000 people in the U.S. are diagnosed with melanoma -- representing about 20 out of every 100,000 -- and 8,700 die.

About 60,000 people are diagnosed each year with Parkinson's disease.

Chen and his colleagues pooled the results of 12 previous studies looking at the association between the two conditions.

All but one study found an increased risk of melanoma among Parkinson's patients.

Of those that reported an elevated chance of melanoma, the risk ranged from about a one-fifth increase to a 20-fold increase among those who had Parkinson's.

When the data from the 12 studies were analyzed together, the chance of Parkinson's patients getting a melanoma diagnosis was two times that of people without Parkinson's.

The results do not hint at whether one of the diseases might cause the other: some people received a diagnosis of melanoma before they were diagnosed with Parkinson's, and others received a diagnosis of the skin cancer afterwards.

Dr. John Bertoni, a professor of neurology and the director of the Parkinson's Disease Clinic at the University of Nebraska Medical Center, said it will be difficult to determine if there is a pattern of one of the diseases preceding the other, because both can take years to develop.

One of Bertoni's studies from 2010 was included in the analysis.

He and his colleagues screened about 2,100 people with Parkinson's disease and found 24 cases of melanoma, which was double what they would have expected to see in the general population (see Reuters Health report from March 8, 2010).

"The next unanswered question is, 'why is this and what can we do about it?'" said Bertoni, who was not an author of the current study.

"Perhaps melanoma and Parkinson's disease could have related pathways," Chen said.

Chen said his group is following up by looking at potential genetic links that might underlie both melanoma and Parkinson's.

"There are no conclusive data at this time," he added.

SOURCE: bit.ly/Q5TNl Neurology, June 7, 2011.