PD link to melanoma bolstered
MedWire News: There is likely to be a genuine increased risk for melanoma among patients with Parkinson's disease (PD), say the authors of a systematic review and meta-analysis.
"One possible explanation for the link between Parkinson's and melanoma is that the two diseases may share some genetic or environmental risk factors," said lead researcher Honglei Chen (National Institute of Environmental Health Services, Research Triangle Park, North Carolina, USA). "However, our understanding of this link is very preliminary."
Chen and team collated the findings of 12 studies on melanoma and PD. They found that, overall, PD patients were 2.11 times more likely to develop melanoma than were people without the condition.
Removal of a study that reported a very high odds ratio (OR) for melanoma among PD patients (20.9) and one reporting a negative association (OR=0.5), eliminated heterogeneity across the studies and produced a 1.8-fold increased risk for melanoma associated with PD.
Before PD diagnosis, patients had a 1.44-fold increased risk for melanoma, relative to people who did not then develop PD, again after exclusion of studies that caused heterogeneity.
After diagnosis, PD patients' risk for melanoma rose to 2.15 times that of people without PD.
The increased risk for melanoma associated with PD was consistent for men and women, despite women having a lower risk for either condition than did men. Nonmelanoma skin cancers were not associated with PD.
Chen and colleagues note that levodopa treatment has been proposed as a possible cause of the increased melanoma risk among PD patients.
"Biologically, such an association is plausible, as exogenous levodopa may stimulate melanogenesis, leading to an accumulation of melanin and hence melanoma growth," they write in the journal Neurology.
But they say that many studies have now refuted such a link, and the increased melanoma risk seen before PD diagnosis in the current study further counts against an effect of levodopa.
Furthermore, the long latency of melanoma, "generally thought to be greater than 10 years," makes it even more unlikely that levodopa treatment contributes to the increased risk for the cancer, says the team.
Chen et al conclude: "Further research is needed to examine the nature and mechanisms of this relationship in order to advance our understanding about the etiology of both diseases."
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By Eleanor McDermid