Association between allergies and cancer incidence: a systematic review and meta-analysis

The prevalence of both allergies and cancer has increased globally. Some evidence suggests that allergies may provide immunological protection against cancer, while studies indicate chronic allergic inflammation could elevate cancer risk. A clearer understanding of their temporal relationship is needed. A systematic literature search following the International Prospective Register of Systematic Reviews (PROSPERO; registration number: CRD42024566792), registered on 08Jul2024, was conducted using PubMed to identify cohort studies published between 1999 and 2024. Various allergic conditions were examined as exposure factors, and both solid and hematological cancers were assessed as outcomes. Subgroup analyses were performed by region, allergy type, and cancer type. Meta-analysis was conducted using pooled odds ratios (ORs) and 95% confidence intervals (CIs). Twenty-eight cohort studies were included. The primary meta-analysis showed a weak positive association between allergies and overall cancer incidence (OR 1.07, 95% CI: 1.03-1.11). Subgroup analysis revealed stronger associations in the Western Pacific, with the strongest association observed in the Western Pacific (OR 1.65, 95% CI: 1.22-2.21). Among allergy types, asthma was significantly associated with increased cancer risk (OR 1.18, 95% CI: 1.10-1.28). Our findings suggest a significant but modest positive association between allergic diseases and cancer incidence. However, due to regional inconsistencies and the limited number of studies in several cancer-specific subgroups, these results should be interpreted with caution. The modest risk increment underscores the need for careful public health evaluation rather than immediate clinical intervention.