ity of California, San Francisco, have put this theory to the test using day care attendance or levels of social activity among other children as a proxy measure of exposure to infectious agents.
The results have been remarkably consistent: The more time spent in day care or engaging in social activity with other children, the lower the risk of childhood leukemia.
"The evidence is indirect but, overall, I believe, persuasive," Dr. Greaves said. "But we still lack unambiguous proof," he continued, such as "identification of a cellular/biochemical mechanism by which an abnormal immune response might trigger and select preleukemic clones."
The situation may be entirely different for infant leukemia, added Dr. Wiemels.Most infant leukemias have a specific translocation involving the MLL gene, and "some people think that it's sufficient to cause cancer," he explained. "It takes less than a year or so to develop the disease, and that may be because the MLL translocation has a strong oncogenic stimulus. So there may not necessarily be a secondary event, at least at the level of DNA mutation."
By Carmen Phillips