Background: A large follow-up study in Denmark showed a two-fold higher incidence of malignant melanoma in patients with Parkinson disease than in the general population. Using a population-based case-control approach, we investigated the prevalence of malignant melanoma, skin carcinoma, and other cancers before a first hospitalization or outpatient visit for Parkinson disease.
Methods: We used the national Danish Hospital Register to identify 8090 patients with a primary diagnosis of Parkinson disease during the period of 1986-1998. Each case was matched with 4 population controls selected at random from among inhabitants alive at the date of first hospital contact with the patient. Incident cases of cancer since 1943 were ascertained by linkage to the Danish Cancer Registry, and the cancer histories of patients with Parkinson disease were compared with those of population controls.
Results: We observed an increased prevalence of malignant melanoma and skin carcinoma prior to the first hospital contact for Parkinson disease, with overall odds ratios of 1.44 (95% confidence intervals = 1.03-2.01) and 1.26 (1.11-1.43), respectively. To the contrary, we observed a reduced prevalence of cancers at smoking-related sites in patients before their first hospital contact for Parkinson disease.
Conclusions: Our finding of an increased prevalence of malignant melanoma and skin carcinoma before the diagnosis of Parkinson disease weakens the suggested hypothesis that these cancers are caused by the treatment of Parkinson disease. The finding of a decreased prevalence of smoking-related cancers preceding Parkinson disease is consistent with the well-known higher risk of Parkinson disease among nonsmokers.