People who suffer from some allergies, such as hives and eczema, may have a higher risk of developing cancers of the blood later in life, a new study suggests.

Although previous studies have suggested that allergies may have the opposite effect and help protect against cancer, Swedish researchers say their findings indicate that certain types of allergies may increase the risk of some blood cancers, such as leukemia and non-Hodgkin’s lymphoma.

"In our study, people with hives showed an increased risk of leukemia," says researcher Karin Söderberg, of the Karolinska Institutet in Sweden, in a news release. "We also found an increased risk of non-Hodgkin's lymphoma among individuals who had eczema during childhood."

Further studies are needed to confirm these results. But experts say the study raises interesting questions about the relationship between diseases that affect the immune system, such as allergies, and the long-term risk of certain blood cancers.

“It should not make people alarmed that just because they have allergies that they could go on to develop malignancies, but it does add thought for future studies,” says Marianne Frieri, MD, PhD, director of allergy immunology at Nassau University Medical Center in East Meadow, N.Y.

Allergies Linked to Cancer?

In the study, which appears in the Nov. 4 issue of the journal BMC Public Health, researchers followed a group of more than 16,000 twins for 31 years. The twins filled out a questionnaire with information on allergies in 1967, and researchers recorded whether they were diagnosed with a blood cancer during the following years.

The study showed that people who reported hives and asthma were about twice as likely to develop leukemia.

Researchers also found an increased risk of non-Hodgkin’s lymphoma among those who had eczema, an allergic disease that affects the skin. Childhood eczema appeared to double the risk of this type of cancer, but researchers say it’s important to point out that the likelihood of developing this rare condition is still very small. The disease affects only about 0.03 percent of people in the U.S.

Other allergic conditions, such as hay fever, were not associated with any increased risk of blood cancer.

Competing Theories, More Study Needed  

Researchers say that a link between allergic diseases and cancer risk has been the subject of several studies, and two possible relationships have been proposed.

The first, known as the immune surveillance hypothesis, holds that allergic conditions may reduce cancer risk by enhancing the ability of the immune system to detect and remove malignant cells.

The second theory argues that conditions that stimulate the immune system, such as allergies, increase the risk of cancer. According to this theory, constant stimulation of the immune system increases the number of disease-fighting white blood cells, which raises the risk of cancer-causing mutations of these cells.

“There is a lot of controversy whether it’s one theory or another,” says Frieri, who is also professor of medicine and pathology at State University of New York at Stony Brook and a fellow of the American College of Asthma, Allergy and Immunology.

Although some studies, including the present Swedish one, have supported both arguments, other studies have also shown no relationship between allergic diseases and cancer risk, or the results were inconsistent.

Researchers say one strength of this study was that the information about allergic diseases and other possible confounding factors was collected after the individuals were diagnosed with cancer, therefore eliminating any potential recall bias. The study also involved a large number of participants who were followed for more than 30 years.

But Frieri points out that there was only a small number of blood cancers reported, which means that random variation in cancer rates cannot be excluded as a possible explanation of the findings. In addition, environmental factors such as exposure to infections may have also played a role.

Frieri says cancer risk is dependent upon many factors and cannot be explained by just allergies. Genes and other environmental, lifestyle, and nutritional factors all contribute to a person’s overall risk of developing cancer.

Söderberg agrees and acknowledges that more research is needed before any conclusive links are drawn between blood cancers and allergies.

“It is plausible that the association between allergic conditions and cancer risk is complex and that the risk of developing cancer could depend on the specific malignancy and could also be influenced by the type of allergic condition,” write Söderberg and colleagues. “Clearly, these conflicting results indicate that this area needs to be investigated further.”

By  Jennifer Warner, reviewed by Brunilda Nazario, MD

SOURCES: Söderberg, K. BMC Public Health, Nov. 4, 2004; vol 4. News release, BioMed Central. Marianne Frieri, MD, PhD, director of the Allergy and Immunology, Nassau University Medical Center in East Meadow, N.Y.; professor of Medicine and Pathology at State University of New York at Stony Brook. American College of Asthma, Allergy and Immunology. American Academy of Allergy, Asthma and Immunology.