Atopic eczema and cancer: parallel cohort studies in England and Denmark

IMPORTANCE: Associations between atopic eczema and cancer are unclear, with competing theories: that increased immune surveillance reduces cancer risk; and that immune stimulation increases risk. Establishing baseline cancer risk in people with atopic eczema is important prior to exploring the impact of new biologic drugs (for eczema) on cancer risk. OBJECTIVE: To investigate whether atopic eczema is associated with cancer. DESIGN: Matched cohort studies (England: 1998-2016; Denmark: 1982-2016). SETTING: English primary care, and nationwide Danish data. PARTICIPANTS: Individuals with atopic eczema (England: adults only; Denmark: any age) matched on age, sex, calendar period, and (in England only) primary care practice, to people without eczema. EXPOSURE: Atopic eczema MAIN OUTCOMES: We compared overall risk of cancer, and of 11 specific cancers, in people with and without eczema. RESULTS: We included 471,970 and 2,239,775 individuals with and without atopic eczema respectively in England; and 44,945 and 445,673 respectively in Denmark. We found little evidence of associations between atopic eczema and cancer overall (adjusted hazard ratios [HRs] [99%CI]: England 1.04 [1.02-1.06]; Denmark 1.05 [0.95-1.16]), or for most specific cancers. However, non-cutaneous lymphoma risk was raised in people with atopic eczema in England (adjusted HR [99%CI] 1.20 [1.07-1.34] for non-Hodgkin’s [NHL] and 1.48 [1.07-2.04] for Hodgkin’s). Lymphoma risk increased with greater eczema severity (NHL adjusted HR [99%CI] compared to without eczema: mild 1.06 [0.90-1.25], moderate 1.24 [1.04-1.48], severe 2.08 [1.42-3.04]). Danish point estimates also showed increased lymphoma in moderate-to-severe eczema compared to without (adjusted HR [99%CI]: NHL 1.31 [0.76-2.26]; Hodgkin’s 1.35 [0.65-2.28]), but confidence intervals were wide. CONCLUSIONS AND RELEVANCE: Our findings, from two large population-based studies in different settings, are largely reassuring as they do not support associations between eczema and most cancers. However, we observed an association between eczema and lymphoma that increased with eczema severity, which warrants further study with the introduction of new therapeutics that may impact cancer risk.