The association between Alzheimer's disease and cancer: Systematic review - Meta-analysis.

The objective of the present study was the quantitative assessment of the previously documented inverse relationship between Alzheimer's Disease (AD) and cancer (CA) by conducting a meta-analysis and evaluating systematic differentiations of the aforementioned relationship based on cancer localization. For the purpose of the study all available empirical data of the last decade, which met specific criteria, were included in the analysis by querying PubMed, Web of Science and Cochrane Library databases. Seven studies were included in the analysis, with a total sample of 18,887 (10,859 AD patients, 8,028 non-demented controls) participants to calculate cancer risk among AD patients, and 11 studies, with a total of 5,607,076 (1,853,318 cancer patients, 3,753,758 healthy controls) participants, were assessed to evaluate AD risk among cancer patients. The analysis revealed that AD patients appear to have a reduced risk of cancer, by 40% (RR 0.60, 95% CI 0.45 - 0.79), while cancer history was associated with a reduced risk of AD, by 15% (RR 0.85, 95% CI 0.77-0.92). Systematic differences were also identified based on site-specific cancer. Indications of heterogeneity and publication bias were present in the analysis. Our meta-analysis is only the fourth conducted on this subject, with newer evidence suggesting a mitigation of the inverse relationship. We emphasize the need for new studies to assess the inverse comorbidity hypothesis, especially in AD patients.