Association of childhood leukaemia with factors related to the immune system

The childhood peak of common acute lymphoblastic leukaemia has been propose d as being a rare response to delayed exposure to a common infection. In th is context, factors related to the child's immune system are of special int erest. information on such factors was obtained in a recent German case-con trol study comprising more than 1000 children with acute leukaemia. Neither being the first-born child, nor a short duration of breastfeeding, indicat ors of a deficit in viral contacts during infancy or the number of infectio us diseases, were significant risk factors. We observed a strong associatio n with fewer routine immunizations with a 3.2-fold increase for those child ren getting less than four immunizations, but this association could parity be explained by reporting bias. While tonsillectomy or appendectomy increa sed the risk of leukaemia in our studies, a protective effect of allergies could be seen. In summary, we found only weak support for the delayed expos ure hypothesis. To some extent this may be due to the chosen surrogate mark ers which reflect, rather indirectly, immunological isolation in infancy an d delayed exposure to common viruses. However, the significant findings for routine immunizations, tonsillectomy and allergies of the child or its par ents merit further investigation.