FRIDAY, July 7, 2017 (HealthDay News) -- People with Parkinson's disease are about four times more likely to develop melanoma skin cancer, and conversely, people with melanoma have a fourfold higher risk of getting Parkinson's, researchers report.
Although doctors have known about the connection between these diseases, they still don't know why having one increases the risk of the other.
"Future research should focus on identifying common genes, immune responses and environmental exposures that may link these two diseases," said study first author Dr. Lauren Dalvin, who's with the Mayo Clinic in Rochester, Minn.
"If we can pinpoint the cause of the association between Parkinson's disease and melanoma, we will be better able to counsel patients and families about their risk of developing one disease in the setting of the other," she said in a Mayo news release.
Parkinson's disease is a progressive brain disorder. Symptoms of the disease include tremors, stiffness and difficulty walking, according to the National Parkinson Foundation.
Melanoma is a form of skin cancer. It occurs much less often than other forms of skin cancer, but causes a large majority of skin cancer deaths, according to the American Cancer Society. Melanoma starts as a new spot on the skin, or when a mole changes in size, shape or color.
Previous studies has suggested that the Parkinson's drug levodopa may play a role in melanoma, but the findings from this new study and others don't support that theory, the researchers said.
The new study included nearly 1,000 people with Parkinson's disease and compared them to almost 3,000 people without the movement disorder. The study also included more than 1,500 with melanoma. All of the study volunteers came from one county in Minnesota.
The researchers said since there is such a strong connection between these diseases, doctors treating patients for either disease should watch for signs of the other. The researchers also recommended that doctors counsel patients about their risk of the other condition.
The study was published in the journal Mayo Clinic Proceedings.
The U.S. National Institute of Neurological Disorders and Stroke has more on Parkinson's disease.