Cancer and Parkinson's disease: the odd couple.

Epidemiological studies have consistently shown that individuals with Parkinson's disease (PD) are less likely to develop nonmelanoma cancers and vice versa. In contrast, the co-occurrence of PD and melanoma has been reported in numerous studies. The exact mechanisms underlying the observed cancer-PD association are not clear. Different hypotheses have been put forward, including shared environmental/lifestyle factors (e.g., smoking and socioeconomic status) and common genetic components (e.g., parkinson protein 2 [PARK2], leucine-rich repeat kinase 2 [LRRK2], Parkinson disease [autosomal recessive, early onset] 7 [PARK7, DJ-1] and pigmentation genes). In the current review, we summarize recent findings to offer new insight into the pathogenesis of both conditions.