Strength of Evidence in Epidemiologic Studies

There is limited/suggestive evidence of an association between exposure to the herbicides considered in this report and spina bifida. There is inadequate or insufficient evidence to determine whether an association exists between exposure to the herbicides and all other birth defects. The evidence regarding association is drawn from occupation and other studies in which subjects were exposed to a variety of herbicides and herbicide components.

Biologic Plausibility

Laboratory studies of the potential developmental toxicity, specifically birth defects, of TCDD and herbicides as a result of exposure to adult male animals are too limited to permit conclusions.

Risk in Vietnam Veterans

Since the strongest associations are from studies of Vietnam veterans and there are some data suggesting that the highest risks were for those veterans estimated to have had exposure to Agent Orange (e.g., Ranch Hands), it therefore follows that there is limited/suggestive evidence for an increased risk in Vietnam veterans of spina bifida in offspring.

Childhood Cancer


In most epidemiologic studies, childhood cancer usually refers to cancer diagnosed from birth through age 15. Childhood cancers are usually classified by primary anatomic site or tumor cell type. The distribution of childhood cancers by type includes leukemia (23 percent), lymphoma (13 percent), central nervous system (19 percent), neuroblastoma (8 percent), soft-tissue sarcoma (7 percent), kidney (6 percent), bone (5 percent), retinoblastoma (3 percent), liver (1 percent), and other (8 percent). There are approximately 6,500 new cases of cancer diagnosed each year in the United States in persons under age 15 (Young et al., 1986). About 2,200 deaths each year result from childhood cancer. Compared with adult cancers, relatively little is known about the etiology of most childhood cancers, and especially about potential environmental risk factors.

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