Treatment with levodopa and risk for malignant melanoma.

A large follow-up study in Denmark of 14,088 patients in whom Parkinson's disease was diagnosed at hospital showed a twofold higher incidence of malignant melanoma in these patients than in the general population. In a nested case-control study of 45 patients with malignant melanoma, 97 patients with nonmelanoma skin cancer, and 172 control subjects, we investigated the hypothesis that treatment with levodopa increases the risk for skin cancer. Information on diagnoses and treatment was retrieved from medical records. We observed a significant fourfold to fivefold increase in the risk for malignant melanoma in a subgroup of patients with a probable diagnosis of idiopathic Parkinson's disease as compared with other patients. There was apparently no effect of levodopa on the risk for malignant melanoma as indicated by an odds ratio of 1.0 (95% confidence interval, 0.8-1.3) per 1,000 g cumulative intake of the drug. We conclude that the increased rate of malignant melanoma observed in patients treated at hospital for Parkinson's disease is restricted to those with idiopathic Parkinson's disease, however, unrelated to the treatment with levodopa.