Of Medicine of the National Academies
23 January 2003
Report Supports Association Between Agent Orange and One Form of
of Medicine Press Release:
-- A re-evaluation of evidence now supports an association between
exposure to herbicides used during the Vietnam War and the development
of a specific form of leukemia in veterans, says a new report from
the Institute of Medicine (IOM) of the National Academies. The report
is the latest update in a series examining the health effects of
defoliants -- including Agent Orange -- and chemicals that contaminate
part of its biennial update, the committee that wrote the report
reassessed six studies of herbicide exposure that provided information
on chronic lymphocytic leukemia (CLL) among other health effects.
The re-examination revealed sufficient evidence of an association
between exposure to chemicals sprayed in Vietnam and risk of developing
previous updates on the health risk to veterans posed by exposure
to Agent Orange and other chemicals used in Vietnam, IOM had considered
all forms of leukemia collectively when examining research on links
between herbicide exposure and risk of cancer. The combined evidence
was found to be inadequate or insufficient to determine whether
any association exists between leukemia and exposure to the herbicides
or their contaminants. However, although classified as a form of
leukemia, CLL shares many traits with Hodgkin's disease and non-Hodgkin's
lymphoma, both of which previously have been found to be associated
with herbicide exposure. Both CLL and lymphomas originate from malignant
B-cells, and CLL can transform into an aggressive non-Hodgkin's
lymphoma known as Richter's Syndrome.
similarities between CLL and lymphomas -- which we have long known
to be associated with exposure to the types of chemicals used in
Agent Orange and other defoliants -- began to raise questions about
whether CLL should be considered separately from other forms of
leukemia," said committee chair Irva Hertz-Picciotto, professor
of epidemiology, University of North Carolina, Chapel Hill, and
University of California, Davis. "At the request of the Department
of Veterans Affairs, we looked into the matter, and our reassessment
indicates that CLL is indeed a special case. The data are sufficient
to support a link between herbicide exposure and this type of cancer."
committee's new assessment of CLL is based on evidence from six
studies that looked at cancer rates, including specific forms of
leukemia, and other health effects among agricultural workers exposed
to herbicides, as well as individuals who resided in agrarian settings.
The risk for CLL was found to be elevated in those whose occupations
involved handling of or exposure to the types of herbicidal chemicals
also used during the Vietnam War.
ability of researchers to pinpoint the health risks faced by individual
veterans is hampered by inadequate information about exposure levels
of troops in Vietnam. Most information comes from studies of civilians
who have been exposed on the job or in industrial accidents to herbicides
or their contaminants. However, most veterans probably experienced
lower levels of exposure than people who have worked with these
chemicals over long periods in occupational or agricultural settings,
and it is difficult to say precisely which troops may have been
exposed to larger amounts.
is the most common form of leukemia, with roughly 7,000 new cases
diagnosed in the United States last year. However, it is among the
rarer forms of cancer, making it difficult to do large-scale studies
to determine causes. There are no accurate estimates of how many
Vietnam veterans have been diagnosed with CLL.
committee's congressionally mandated report also reaffirms findings
from previous IOM updates. In addition to non-Hodgkin's lymphoma,
Hodgkin's disease, and now CLL, there is sufficient evidence of
a link between exposure to chemical defoliants or their contaminants
and the development of soft-tissue sarcoma and chloracne in veterans.
Also, scientific studies continue to offer limited or suggestive
evidence of an association with other diseases in veterans -- including
Type 2 diabetes, respiratory cancers, prostate cancer, and multiple
myeloma -- as well as the congenital birth defect spina bifida in
forces sprayed Agent Orange and other defoliants over parts of south
Vietnam and Cambodia beginning in 1962. Most large-scale sprayings
were conducted from airplanes and helicopters, but considerable
quantities of herbicides were dispersed from boats and ground vehicles
or by soldiers wearing back-mounted equipment. A 1969 scientific
report concluded that one of the primary chemicals used in Agent
Orange could cause birth defects in laboratory animals. The U.S.
military therefore suspended the use of Agent Orange in 1970 and
halted all herbicide spraying in Vietnam the following year.
committee's work is sponsored by the U.S. Department of Veterans
Affairs. The Institute of Medicine is a private, nonprofit institution
that provides health policy advice under a congressional charter
granted to the National Academy of Sciences. A committee roster