Wednesday, May 19, 2010

Childhood Leukemia: Environmental Toxins and Pesticides in Cancer Risk

Much media attention has focused lately on the links between environmental exposures and cancer risk (see related post), and a new study out this month further confirms the confined effects such exposures seem to have on the risk of cancer.

In a new study published this month in the journal Cancer Causes and Control, researchers report on a very detailed review of the published studies addressing occupational exposure to pesticides and the risk of childhood leukemia (see Van Maele-Fabry et al, 2010).  All studies published through July of 2009 are included in this systematic review of evidence. Established methods are used to combine the results from 25 studies.

From this extensive analysis we see that occupational exposure to pesticides among women increases the risk of childhood leukemia in their children. However, there was no association for exposure of the father and risk of leukemia. Importantly, the report evaluated the timing of exposure specifically addressing exposure before pregnancy, during pregnancy, and after pregnancy. Risk was elevated for exposure both before and during pregnancy. For women, exposure to insecticides, herbicides, and fungicides increased risk. While occupational exposure was associated with risk, a more general classification of "farming" was not related to risk.

These occupational data suggest that the specific exposure to pesticides, rather than merely an assumption from the classification of occupation, is necessary to uncover the relations between exposure to pesticides and risk of childhood leukemia.

Another rigorous study that evaluated the relation between environmental occupational exposures and cancer was reported some five years ago (see Boffetta, 2004). This report also rigorously reviewed the published literature through 2002. Boffetta concluded that approximately 2 percent of cancer is caused by occupational exposures. While much concern in the recent report from the President’s Cancer Panel focused on the fact that the early estimates of the proportion of cancer caused by environmental exposures by Doll and Peto had not been updated since 1980, these two reports exemplify the substantial body of research that has continued to quantify the impact of occupational and environmental exposures on the cancer burden in society.

With these rigorous updates, we are reassured that the estimates continue to support a burden that is in the range of 4 to 6% of cancers caused by occupational and environmental exposures.  This makes such exposures an important cause of cancer, to be sure, but one that is responsible for a much smaller percentage of cancers compared to lifestyle factors like tobacco use and obesity.

Works cited:
Van Maele-Fabry G, Lantin AC, Hoet P, & Lison D (2010). Childhood leukaemia and parental occupational exposure to pesticides: a systematic review and meta-analysis. Cancer causes & control : CCC, 21 (6), 787-809 PMID: 20467891

Boffetta, P. (2004). Epidemiology of environmental and occupational cancer Oncogene, 23 (38), 6392-6403 DOI: 10.1038/sj.onc.1207715

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