Immune Development May Play a Role in the Expression of Childhood Leukemia

NEW YORK MAR 25, 2008 (Reuters Health) - Early immunologic challenge may play a role in the expression of childhood leukemia, according to Canadian researchers reporting in the March 1st issue of the American Journal of Epidemiology.

"Current hypotheses in the etiology of childhood leukemia suggest a role for immune development and response to infection, although a specific infectious agent has yet to be implicated," Dr. Mary L. McBride, of British Columbia Cancer Agency, Vancouver, and colleagues write.

The researchers examined the association between childhood leukemia and several clinical, environmental, and genetic risk factors. This included the effect of postnatal exposures predicted to affect early immune development, such as childhood vaccinations, illness, medication use, and breastfeeding patterns.

A total of 399 leukemia cases were identified through pediatric oncology centers and population-based cancer registries, and each case was matched by age, gender and region to a control. Information on risk factors was collected through interviews with each child"s parents or guardians.

An association was observed between vitamin supplementation and an excess risk of leukemia (OR = 1.66). Use of immunosuppressant medication was associated with a decreased risk of leukemia (OR = 0.37).

Breastfeeding for more than 6 months was also protective against leukemia (p < 0.05).

The team did not uncover any association with common childhood illnesses, or for most common vaccines. "We observed a protective effect of MMR vaccination on childhood leukemia, but only among children immunized after 1 year of age, and odds ratios were only marginally significant (p < 0.10)," Dr. McBride"s team explains.

They conclude: "Our results are congruent with the current hypothesis put forth by Greaves that states that reduced antigenic challenge during early postnatal development may contribute to an increased risk of childhood leukemia. Information on risks associated with immunosuppressant medication and vitamin supplementation in relation to the timing of exposure (infancy vs. later childhood) strengthens the interpretation of our results in accordance with Greaves hypothesis."

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