Malignant melanoma and levodopa in Parkinson's disease: causality or coincidence?

Levodopa is the major drug used in the treatment of patients with Parkinson's disease. However, levodopa continues to be 'contra-indicated' for patients with Parkinson's disease associated with malignant melanoma. Case reports have suggested that levodopa has a causal relationship with malignant melanoma due to their shared dopamine biochemical pathway. Clinical characteristics of 54 patients with both Parkinson's disease and melanoma were analyzed (43 cases from the literature and 11 from our institution). The results suggest that the occurrence of both Parkinson's disease and melanoma in these patients is coincidental rather than causal. It did not appear that the Parkinson's disease patients on levodopa therapy were predisposed to melanoma, nor did levodopa therapy appear to exaggerate melanoma if it were previously present.