Are cancer and allergy mutually exclusive?: Myths and difficulties

Researchers are asking the question: are there relationships between atopic illnesses and cancer? There are many papers concluding that patients with atopy or asthma have less cancer than those who do not. Unfortunately, almost the same number of papers concludes the contrary. This month we summarize two papers that report on the effort to discover the possible association between atopy and leukemia or ovarian cancer.

In the first of two articles, ElMasri et al. (Archives of Environmental and Occupational Health, 2010, 65:101-105) report the results of a case-control study that looks at association between asthma and ovarian cancer, using a statewide Florida hospital discharge database. The authors started with asthma (present vs. absent) as their risk factor variable, and with ovarian cancer (present vs. absent) as the dependent variable. They found that patients with ovarian cancer were 30% less likely to be diagnosed with asthma compared to limb fracture patients and 38% less likely to be diagnosed with AMI, suggesting that patients with asthma were less likely to develop cancer of the ovary. Based on these results, ElMasri and co-authors suggest an IL-4 link to the apparent protective effect of asthma, which has been shown to have tumor inhibition activity. Zuber Mulla, PhD, CPH, FAAAAI, senior author on the paper, notes, "We originally looked at other allergic conditions during this retrospective study such as hay fever but naturally this condition was probably undercoded in these types of databases so we dropped it and focused on a more serious condition, asthma (but only 40% or so of asthma is allergic asthma--so more work is still needed in this area)."

Linabery et al. (American Journal of Epidemiology 2010, 171:749-764) present findings from a broader scope meta-analysis that examined associations between clinical manifestations of atopy, including allergies, asthma, eczema, “hay fever,” and hives, and childhood/adolescent leukemia, acute lymphoblastic leukemia (ALL) and acute myeloid leukemia (AML). Ten case-control studies were identified from multiple databases. For any atopy/allergies, 31% were less likely to develop ALL. Each individual atopic disease also had a significant inverse association with ALL. The authors find that an inverse relationship exists between any atopy/ allergy and AML, but that it does not reach significance. There was no overall association between any atopy/allergy and any leukemia. They also discuss the controversy over the protective versus predisposing effect of atopy with respect to cancer. On one side, atopy is hypothesized to be protective, pointing to increased immune responses leading to increased immune surveillance. The opposing position argues that increased immune responses lead to hyperproliferation, which increases the likelihood of genetic errors, such as oncogene dysregulation. Linabery et al. point out that the commonality shared by both atopy and leukemia is the working hypothesis that both are linked to the maturation rate of the immune system.

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