Cancer risk in Parkinson disease: An updated systematic review and meta-analysis

Background and purpose: Increasing evidence suggests significant associations between Parkinson disease (PD) and cancer risks. We conducted an updated review of studies that examined the risks of various cancer among PD patients and how this differed when cancer preceded PD diagnosis or PD diagnosis preceded cancer. Methods: Four databases were searched for studies that examined the association between PD and incidence of cancer from database inception to 4 June 2021. Three independent reviewers screened the articles for eligibility and extracted study data. Pooled relative risk with 95% confidence intervals were calculated using a random effects model. Results: Forty studies involving 11 case–control studies, two nested case–control studies, 22 cohort studies, and five cross-sectional studies were included. Compared to controls, PD patients had lower risks of lung, genitourinary, gastrointestinal, and haematological cancers. Conversely, higher risks of melanoma and brain cancer were noted among PD patients. No association was found between PD and risk of female cancers. Subgroup analysis found negative associations between PD patients and risks of colon cancer, rectal cancer, and non-Hodgkin lymphoma. Conclusions: Findings from our meta-analysis suggest PD patients had lower risks of lung, genitourinary, gastrointestinal, and haematological cancers and increased risks of melanoma and brain cancer. Future research to investigate the underlying mechanisms between PD and cancers is warranted.