Link found between Agent Orange and chronic lymphocytic leukaemia
Charles Marwick Washington, DC
Reviewing recently published scientific evidence, a committee of the US
Institute of Medicine has concluded that a positive association exists between
exposures to herbicides used as defoliants from 1962 to 1971during the Vietnam
war and the risk of developing chronic lymphocytic leukaemia.
The report is the fourth in a series of reviews that the institute has
conducted at Congresss request since 1996 of the health effects of these
defoliants. Earlier reports had linked Hodgkins disease and non-Hodgkins
lymphoma with exposure to these defoliants. Chronic lymphocytic leukaemia shares
many traits with these disorders.
As both chronic lymphocytic leukaemia and lymphomas originate from malignant
B cells and the former can transform into Richters syndromea particularly
aggressive form of non-Hodgkins lymphomathe committee wondered whether chronic
lymphocytic leukaemia should be considered separately from other forms of
leukaemia.
Irva Hertz-Picciotto of the School of Public Health, University of North
Carolina, Chapel Hill, and chairwoman of the committee, said: "We looked into
the matter, and our reassessment indicates that CLL [chronic lymphocytic
leukaemia] is indeed a special case. The data are sufficient to support a link
between herbicide exposure and this type of cancer."
The committees assessment is based on evidence from six studies that looked
at cancer rates and other health effects among agricultural workers and farm
community residents exposed to herbicides. The panel found that the incidence of
chronic lymphocytic leukaemia was raised in those whose occupations involved
handling of or exposure to the types of herbicides that were used during the
Vietnam War.
"There is a positive association between herbicides and the outcome in which
chance, bias and confounding could be ruled out with reasonable confidence," the
committee wrote.
The principal defoliant used by the US military forces in Vietnam was a
mixture of 2,4-dichlorophenoxyacetic acid (2,4-D), 2,4,5-trichlorophenoxyacetic
acid (2,4,5,-T), and one form of dioxin, TCDD
(2,3,7,8-tetrachlorodibenzo-p-dioxin), present as contaminant. The defoliant is
popularly known as Agent Orange, from the identifying colour of the drums in
which it was stored.
The committee conclusions are important to those who served in Vietnam as, if
they develop chronic lymphocytic leukaemia, they will be eligible for disability
benefits. According to the US Veterans Administration, which provides these
benefits, there are about 500 new cases annually.
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