Review of case-control studies related to breastfeeding and reduced risk of childhood leukemia.

OBJECTIVE To conduct a systematic review to evaluate the evidence for the effect of breastfeeding on the risk of developing childhood leukemia. REVIEW METHODS We sought studies providing data regarding the association of breastfeeding and occurrence of childhood leukemia. Studies were identified by using Medline, HHS Blueprint for Action on Breastfeeding, US Department of Health and Human Services Office on Women's Health, Cochrane Database of Systematic Reviews, National Centre for Reviews and Dissemination, reference lists, and national experts. Methodologic quality was evaluated for each study by using criteria from the US Preventive Services Task Force and the National Health Service Centre for Reviews and Dissemination. RESULTS We reviewed 111 citations to identify 32 potentially eligible full-text articles. Of the 10 studies reviewed, only 4 were sufficient to provide at least fair-quality evidence regarding the association between maternal breastfeeding and childhood leukemia. Studies conflicted regarding the protective effect of breastfeeding on childhood leukemia. In the 2 largest and highest quality studies, breastfeeding was associated with a significant risk reduction in one study with longer breastfeeding duration, reflecting greater protection, and a nonsignificant but suggestive difference in the other. Taken together, half of the studies associated breastfeeding with a lower risk of acute lymphocytic leukemia. CONCLUSIONS There are few high-quality studies that examine the potential for a protective effect of breastfeeding for childhood leukemia. Furthermore, the few studies that exist disagree regarding the association. It is estimated that the United States spends 1.4 billion dollars annually on the treatment of childhood leukemia. Patients, clinicians, and policy makers do not have the data that they need to make decisions regarding this important potential preventive measure.