Eczema and cancer risk: a critical appraisal and review of the literature

Eczema as a protective factor for brain cancer: a meta-analysis

BACKGROUND

Brain cancer is one of the most aggressive cancer types owing to poor treatment effects. Epidemiological studies have demonstrated that allergies may increase the disease risk. Therefore, this study evaluated the association between eczema and the risk of various brain cancers.

METHODS

We systematically searched the PubMed and Embase databases from their inception until June 23, 2022. Two reviewers independently reviewed and screened the articles, extracted data, assessed the study quality, and pooled the results. Stata software was used to generate pooled odds ratios and 95% confidence intervals (CIs).

RESULTS

We included 20 studies comprising 5,117,222 patients that investigated the relationship between eczema and brain cancer. Eczema was significantly inversely associated with the risk of brain cancer (odds ratio [OR], 0.82; 95% CI, 0.77-0.87), glioma (OR, 0.53; 95% CI, 0.14-2.02), meningioma (OR, 0.74; 95% CI, 0.66-0.84), and acoustic neuroma (OR, 0.60; 95% CI, 0.41-0.88). Interesting, The strong correlation between eczema and the reduced risk of brain cancer was observed in people over 16 years old (OR, 0.79; 95% CI, 0.71-0.88), but not in those under 16 years old (OR, 0.94; 95% CI, 0.79-1.11). In addition, subgroup analyses found that eczema significantly decreased the glioma risk in Europeans (OR, 0.73; 95% CI, 0.65-0.82) but not Australians (OR, 0.53; 95% CI, 0.14-2.02) or Americans (OR, 1.01; 95% CI, 0.69-1.46).

CONCLUSION

Eczema may be considered as a potential protective factor of brain cancer in population aged over 16 years. However, this relationship requires verification using large-scale clinical data.

Epidermal barrier defects link atopic dermatitis with altered skin cancer susceptibility

Atopic dermatitis can result from loss of structural proteins in the outermost epidermal layers, leading to a defective epidermal barrier. To test whether this influences tumour formation, we chemically induced tumours in EPI−/− mice, which lack three barrier proteins—Envoplakin, Periplakin, and Involucrin. EPI−/− mice were highly resistant to developing benign tumours when treated with 7,12-dimethylbenz(a)anthracene (DMBA) and 12-O-tetradecanoylphorbol-13-acetate (TPA). The DMBA response was normal, but EPI−/− skin exhibited an exaggerated atopic response to TPA, characterised by abnormal epidermal differentiation, a complex immune infiltrate and elevated serum thymic stromal lymphopoietin (TSLP). The exacerbated TPA response could be normalised by blocking TSLP or the immunoreceptor NKG2D but not CD4+ T cells. We conclude that atopy is protective against skin cancer in our experimental model and that the mechanism involves keratinocytes communicating with cells of the immune system via signalling elements that normally protect against environmental assaults.

DOI:http://dx.doi.org/10.7554/eLife.01888.001

Skin cancer is a common and growing problem—according to the World Health Organization, skin cancers account for one in every three cancers diagnosed world wide. There is some evidence from epidemiological studies that patients with certain allergies might be protected against cancer and, in particular, that the allergic skin condition atopic dermatitis is associated with reduced levels of various skin cancers. However, it is difficult to know if this reduction is due to the atopic dermatitis itself or to the drugs used to treat this allergy.

Genetically engineered mice that are lacking three proteins that are involved in the formation of the cornified envelope—the protective layer that replaces the normal plasma membrane in the cells of the outermost skin layers—can be used to study atopic dermatitis. These ‘triple knockout mice’ have a defective epidermal barrier and altered levels of immune T-cells in the skin.

Now Cipolat et al. have investigated whether defects in the epidermal barrier protect against skin cancer. Knockout mice and wild-type mice were treated with two chemicals: DMBA, which causes mutations in a gene called HRas, and TPA, which promotes the formation of tumours from cells that contain HRas mutations. After about 16 weeks almost all of the wild-type mice had at least one benign tumour, whereas half of the knockout mice had no tumours. Overall, the average number of benign tumours per mouse was six times higher in the wild-type mice. This shows that the mutations that cause the epidermal barrier defects in knockout mice also protect them against the tumours caused by the combined effects of DMBA and TPA.

Cipolat et al. then compared how the mice responded to DMBA or TPA alone. The knockout mice and the wild-type mice responded to DMBA in the same way; however, the knockout mice showed an exaggerated response to TPA, including a strong inflammatory reaction. This response comprised the production of higher levels of various proteins that are involved in communications between skin cells and the immune system. Cipolat et al. propose that the immune reaction caused by this exaggerated response could help to prevent tumour formation by eliminating tumour-forming cells in the skin.

DOI:http://dx.doi.org/10.7554/eLife.01888.002

Nonallergic comorbidities of atopic eczema: an overview of systematic reviews

The aims of this overview are to synthesize the current evidence of published systematic reviews (SRs) on nonallergic comorbidities of atopic eczema (AE). EMBASE and MEDLINE were searched for SRs published from inception to November 2012. SRs were selected independently based on predefined inclusion criteria. Methodological quality of SRs included was assessed by two independent reviewers using the Revised Assessment of Multiple Systematic Reviews (R-AMSTAR) checklist. Nine SRs met all inclusion criteria. Six reviews addressing the association between AE and cancer suggest a decreased risk of glioma, meningioma, and acute lymphoblastic leukemia in patients with current or previous AE. One SR reported a consistent positive association of AE with attention-deficit hyperactivity disorder (ADHD). Diabetes mellitus type 1 and multiple sclerosis (MS) were not significantly related to AE in reviews based on cross-sectional and case-control studies. Patients with AE appear to be at decreased risk of brain tumors. The relationship of AE with Th1- and Th17-mediated (auto-)inflammatory conditions such as diabetes mellitus type 1 and MS should be clarified in prospective observational studies. Children with AE are at increased risk of ADHD. SRs on the risk of depression and Th17-mediated disorders such as inflammatory bowel disease of patients with AE are missing.

Comorbidity in Atopic Dermatitis

The negative impact of atopic dermatitis (AD) often extends beyond the skin. Children with AD experience increased rates of infectious, mental health, and allergic diseases compared to their non-atopic peers. The mechanisms underlying these associations remain elusive. New insights from genetic and epidermal research pinpoint the skin barrier as a primary initiator of AD. Epicutaneous sensitization represents an intriguing new model which links a disrupted skin barrier to the later development of IgE-mediated diseases in patients with AD. Recent epidemiological studies have identified new comorbidities linked to AD as well, including several mental health disorders and obesity. This manuscript reviews the recent literature regarding both classic and newly described AD comorbidities.