Cancer Risk in Parkinson's Disease: An Updated Systematic Review and Meta-Analysis

Background Increasing evidence suggests significant associations between Parkinson's 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 June 4th , 2021. Three independent reviewers screened the articles for eligibility and extracted study data. Pooled relative risk (RRs) with 95% confidence interval (CI) were calculated using random-effects model. Results Forty studies involving 11 case-control studies, 2 nested case-control studies, 22 cohort studies and 5 cross-sectional studies were included. Compared to controls, PD patients had lower risks of lung cancer and genitourinary cancers, gastrointestinal cancers 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. Conclusion Findings from our meta-analysis suggest PD patients had lower risks of lung cancer, genitourinary cancers, gastrointestinal cancers and haematological cancer and increased risks of melanoma and brain cancer. Future research to understand the underlying mechanisms between PD and cancers are warranted.