Melanoma often seen before Parkinson's disease

NEW YORK, Sep 27 (Reuters) Rates of malignant melanoma and skin cancer are increased before a diagnosis of Parkinson's disease, new research suggests. This casts doubt on the notion that levodopa therapy for Parkinson's disease may contribute to the observed higher risk of malignant melanoma in such patients.

Dr Jorgen H Olsen and colleagues from the Institute of Cancer Epidemiology, Copenhagen, Denmark, examined the prevalence of malignant melanoma, skin carcinoma, and other cancers before a first hospitalization or outpatient visit for Parkinson's disease. A total of 8090 patients were included in the analysis.

Each ''case subject'' was matched to four randomly selected controls who were alive at the index date of their respective cases.

The authors compared the cancer histories of Parkinson's disease patients with those of the controls.

Of the Parkinson's disease patients, 966 (roughly 12 percent) had a total of 1020 cancers diagnosed before being diagnosed with Parkinson's disease.

A total of 3734 (11.5 percent) of 32,320 controls had a total of 4072 cancers diagnosed before the index date.

Subjects who had an eventual diagnosis of Parkinson's disease had a slightly higher prevalence of cancer at any site compared to controls.

Furthermore, the prevalence of malignant melanoma was 44 per cent higher and the prevalence of skin carcinoma was 26 percent higher in patients with Parkinson's disease compared with controls.

Since the 1970s, a number of case reports have suggested that levodopa therapy for Parkinson's disease increases the risk of skin cancer. It was hypothesised that levodopa could trigger or activate melanoma by sharing the biosynthetic pathway of melanin.

The current findings, Olsen and colleagues conclude, appear to weaken the hypothesis that levodopa is causally related to an increased risk of malignant melanoma.

SOURCE: Epidemiology September 2006.

REUTERS DKB VC0940