PARK2 has been identified as a potent tumour suppressor gene, whereas mutations in LRRK2 have been associated with an increased risk of cancer.8 While a positive, bidirectional link between PD and melanoma, a malignant tumour that develops from melanocytes is well documented,9 there appears to be an inverse association between PD and total cancer.10 However, it remains unclear whether PD and cancer are associated mechanistically, or the findings were confounded by other factors, such as study designs and smoking. This evidence concerns the gene PRKN and Parkinson disease.