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Atopic eczema wasn't tied to a significantly increased risk for most cancers, according to research from England and Denmark.

In an English matched-cohort of nearly 500,000 individuals with atopic eczema, there was little evidence to suggest an association between eczema and overall cancer incidence (adjusted hazard ratio [aHR] 1.04, 99% CI 1.02-1.06), reported Kathryn Mansfield, PhD, of the London School of Hygiene and Tropical Medicine (LSHTM), and colleagues.

Similar findings were seen in a Danish matched-cohort of nearly 50,000 people with atopic eczema (HR 1.05, 99% CI 0.95-1.16), the group wrote in .

"On the whole, our findings are reassuring. For most cancers, we didn't see any increased cancer risk for people with atopic eczema compared to people without atopic eczema," Mansfield and co-author Sinéad Langan, PhD, also of LSHTM, jointly told MedPage Today.

"The existing research exploring whether there is a link between having atopic eczema and cancer was conflicting, and some of the existing studies were small and weren't able to investigate whether having eczema came before a cancer diagnosis," they stated, adding that this study is of particular clinical importance because new biologic treatments for atopic eczema -- some of which may affect cancer risk -- are coming to market.

However, in the English cohort, there was a modestly increased risk for developing noncutaneous lymphoma among people with eczema. Specifically, those with eczema saw a 19% (aHR 1.19, 99% CI 1.07-1.34) elevated risk for non-Hodgkin's lymphoma, as well as a 48% (aHR 1.48, 99% CI 1.07-2.04) increased risk for Hodgkin's lymphoma.

Risk of non-Hodgkin's lymphoma seemed to be dependent on eczema severity, with the highest risk seem among those with severe cases of eczema when compared to those free of eczema:

• Mild eczema: aHR 1.06 (99% CI 0.90-1.25)
• Moderate eczema: aHR 1.24 (99% CI 1.04-1.48)
• Severe eczema: aHR 2.08 (99% CI 1.42-3.04)

There were some similar associations seen among the Danish cohort, linking lymphoma risk to moderate and severe cases of eczema, though the results didn't reach statistical significance.

"I don't think we really had any strong expectations about what we would find as the existing research was so contradictory," said Mansfield and Langan.

"However, we were surprised to see that both Hodgkin's and non-Hodgkin's lymphomas were more likely in people with atopic eczema compared to people without," they added, pointing out that these two types of lymphoma typically occur in very different people. "Therefore, we feel that the link we found between eczema and lymphoma needs more research to understand the underlying reasons for the increased lymphoma risk."

As for these future studies, one avenue to explore should focus on the presence of the Epstein-Barr virus in people with atopic eczema, the researchers suggested.

They underscored that overall occurrence of lymphomas are rare, so even if the link does indeed exists between eczema and these cancers, the risk still remains very small.

The English cohort included 471,970 adults from 1998 to 2016 with atopic eczema matched with over 2.2 million adults who were free of eczema based on age, sex, time period, and primary care practice. The Danish cohort included 44,945 individuals of all ages (median age 13.7) from 1982 to 2016 with atopic eczema matched with 445,673 individuals without eczema. Anyone with a history of cancer, other than nonmelanoma skin cancer or keratinocyte cancer, were excluded.

In addition to lymphoma, the researchers tested for associations between eczema and melanoma, multiple myeloma, leukemia, and cancers of the lung, breast, prostate, pancreas, and central nervous system.

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