Alzheimer disease and cancer risk: a meta-analysis

Alzheimer disease (AD) and cancer are seemingly two opposite ends of one spectrum. Studies have suggested that patients with AD showed a reduced risk of cancer and vice versa. However, available evidences are not conclusive. So we conducted a meta-analysis using published literatures to systematically examine cancer risk in AD patients.

A PubMed, EMBASE, and Web of Science search were conducted in May 2014. Pooled risk ratios (RRs) with their corresponding 95 % confidence intervals (CIs) were obtained using random-effects meta-analysis. We tested for publication bias and heterogeneity, and stratified for study characteristics, smoking-related cancers versus nonsmoking-related cancers, and site-specific cancers.

Nine studies were included in this meta-analysis. Compared with controls, the pooled RR of cancer in AD patients was 0.55 (95 % CI 0.41-0.75), with significant heterogeneity among these studies (P < 0.001, I(2) = 83.5 %). The reduced cancer risk was more substantial when we restricted analyses to cohort studies, studies with adjusted estimates, studies defining AD by generally accepted criteria, and studies with longer length of follow-up. In sub-analyses for site-specific cancers, only lung cancer showed significant decreased risk (RR 0.72; 95 % CI 0.56-0.91). We did not find significant publication bias (P = 0.251 for Begg and Mazumdar's test and P = 0.143 for Egger's regression asymmetry test).

These results support an association between AD and decreased cancer risk.