An analysis shows that people who suffer from Parkinson's disease face up to twice the risk of developing melanoma - the dangerous form of skin cancer.
Previous research has shown mixed results, but the meta-analysis by the National Institute of Environmental Health Sciences and published in the journal Neurology showed a significantly higher risk of melanoma in Parkinson's patients.
Men with Parkinson's are twice as likely to develop melanoma, the most dangerous form of skin cancer, and women with Parkinson's were 1.5 times as likely to receive the same diagnosis.
There was no link observed between non-melanoma skin cancer and Parkinson's in the dozen studies which spanned 1965 to 2010.
Since the studies were small in size, most showing fewer than 10 cases of people with both conditions, it was difficult to draw individual conclusions. However, the meta-analysis showed a distinctly increased risk.
"Parkinson's disease patients in general have a lower risk for cancer, smoking-related cancers in particular, but they may have a higher risk for melanoma," said study author Honglei Chen.
"One possible explanation for the link between Parkinson's and melanoma is that the two diseases may share some genetic or environmental risk factors," Chen said. "However, our understanding of this link is very preliminary."
Worldwide estimates of the number of people living with Parkinson's, a brain disease that causes physical tremors and difficulty with movement and balance, range from five to 10 million.
About 132,000 melanoma skin cancers occur globally each year, according to the World Health Organization.