People with Parkinson’s Disease appear to have a significantly higher risk of melanoma, according to findings from a meta-analysis (a "study of studies") reported in the June 7 print issue of Neurology. While researchers had long suspected such a link, this is the first study to bring together previous research to achieve statistically significant results.
Melanoma is the most deadly form of skin cancer. While it only accounts for five percent of all skin cancers, it leads to the vast majority of skin cancer deaths -- nearly 9,000 per year in the United States. About 70,000 Americans are diagnosed with melanoma each year. Parkinson’s Disease affects nearly one million people in the United States. It is a progressive neurodegenerative disorder that affects characterized by tremors, problems with walking and movement, slowed gait, and difficulties with balance and coordination.
The research team, led by Honglei Chen, M.D., PhD. of the National Institute of Environmental Health Sciences, a division of the National Institutes of Health, searched for previous studies that had been designed to investigate possible links between Parkinson’s and melanoma. They found 12 studies that fit their criteria, all of which had been conducted between 1965 and 2010. In most of the studies, fewer than 10 people had both Parkinson’s and melanoma, not enough for researchers to establish a significant association between the two conditions. By combining the study results and using a statistical technique called meta-analysis, which allows researchers to combine, summarize, and review previous research, Chen’s team was able to establish statistically significant associations.
The associations were surprisingly strong. Women with Parkinson’s disease were one-and-a-half times more likely to also have a diagnosis of melanoma as were women without the disease. The link was even stronger among men: Men with Parkinson’s were twice as likely to have been diagnosed with melanoma as were their Parkinson’s-free peers. No clear link was found between Parkinson’s and other types of skin cancer.
It's unclear why melanoma may affect people with Parkinson's disease more frequently -- and vice-versa. Chen's team also found that people with melanoma were more likely to develop Parkinson's, confirming findings presented in 2009 at the American Academy of Neurology annual meeting. In that study, a research team from Harvard School of Public Health found that people who had a sibling or parent who had been diagnosed with melanoma were twice as likely to develop Parkinson's disease as the general population.
Chen's team noted that most of the people with Parkinson's Disease also had at least one or two of the 13 risk factors for melanoma:
- blue eyes
- fair complexion
- severe blistering sunburn in childhood
- sun sensitivity
- blonde or red hair
- other skin cancer (past or present)
- large or irregular pigmented lesions
- congenital moles
- family history of melanoma
- changes in moles
- prior melanoma
The majority (90 percent) of people with Parkinson's were taking levo-dopa, a drug commonly used to treat Parkinson's disease. At one time, some researchers speculated that levo-dopa could increase the risk of melanoma. However, previous studies have shown no association betweeen the two conditions.
Researchers emphasized that their findings do not suggest that Parkinson’s causes melanoma, nor vice-versa. One possible interpretation of the results is that the two conditions might share some genetic and environmental risk factors.
Ultimately, the findings suggest that people with Parkinson's need to take extra steps to protect themselves from the sun. The National Parkinson Foundation has recommended since 2009 that people with Parkinson's disease wear sunscreen, limit sun exposure, and schedule a yearly appointment with a dermatologist.
Gao X, Simon KC, Han J, Schwarzschild MA, Ascherio A. Family history of melanoma and Parkinson disease risk. Neurology. 2009 Oct 20;73(16):1286-91.
Liu, R., Gao, X., & Chen, H. (2011). "Meta-analysis of the relationship between Parkinson disease and melanoma." Neurology June 7, 2011 vol. 76 no. 23. doi: 10.1212/WNL.0b013e31821e554e
Okun, M.S. (2009). "Time for Parkinson's disease patients to break out the suntan lotion: Increased risk of melanoma in Parkinson's disease." National Parkinson Foundation. Available at http://www.parkinson.org/NationalParkinsonFoundation/files/b5/b560dec7-b...