Institute of Medicine Report Supports Association Between 
Agent Orange and Chronic Leukemia (CLL) 

National Academy of Sciences/Institute of Medicine PRESS RELEASE 23jan03

WASHINGTON -- 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 them.

As 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 CLL.

In 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.

"The 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."

The 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.

The 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.

CLL 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.

The 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 veterans' children.

U.S. 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.

The 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 follows.

Read the full text of Veterans and Agent Orange: Update 2002 for free on the Web as well as over 2,500 other publications from the National Academies. Printed copies will be available for purchase from the National Academies Press; tel. (202) 334-3313 or 1-800-624-6242 or on the Internet at http://www.nap.edu. Reporters may obtain a pre-publication copy from the Office of News and Public Information (contacts listed above).

INSTITUTE OF MEDICINE Board on Health Promotion and Disease Prevention

Committee to Review the Health Effects in Vietnam Veterans of Exposure to Herbicides (Fourth Biennial Update)

Irva Hertz-Picciotto, Ph.D. (chair) Associate Professor Department of Epidemiology and Preventive Medicine University of California, Davis, and Professor Department of Epidemiology School of Public Health University of North Carolina Chapel Hill

Kiros T. Berhane, Ph.D. Assistant Professor Department of Preventive Medicine University of Southern California Los Angeles

Margit L. Bleecker, M.D., Ph.D. Director Center for Occupational and Environmental Neurology Baltimore

Paul F. Engstrom, M.D. Senior Vice President for Population Science, and Medical Director Fox Chase Network Philadelphia

Richard A. Fenske, Ph.D., M.P.H. Director Pacific Northwest Agricultural Safety and Health Center, and Professor of Environmental Health Industrial Hygiene and Safety Program School of Public Health and Community Medicine University of Washington Seattle

Thomas A. Gasiewicz, Ph.D. Professor and Chair Department of Environmental Medicine, and Deputy Director Environmental Health Sciences Center School of Medicine University of Rochester Rochester, N.Y.

Tee L. Guidotti, M.D., M.P.H. Professor and Chair Department of Environmental and Occupational Health School of Public Health and Health Services, and Director Division of Occupational Medicine and Toxicology Department of Medicine School of Medicine and Health Science George Washington University Washington, D.C.

Loren D. Koller, D.V.M., Ph.D. Consultant Environmental Health and Toxicology Corvallis, Ore.

John J. Stegeman, Ph.D. Senior Scientist and Chair Department of Biology Woods Hole Oceanographic Institution Woods Hole, Mass.

David S. Strogatz, Ph.D., M.S.P.H. Associate Professor and Chair Department of Epidemiology School of Public Health State University of New York Albany

INSTITUTE STAFF

Michelle Catlin, Ph.D. Study Director

Contacts: Christine Stencel, Media Relations Officer Andrea Durham, Media Relations Assistant Office of News and Public Information (202) 334-2138; e-mail news@nas.edu 

Agent Orange Linked to One Form of Leukemia, U.S. Study Says 

JOHN LAUERMAN / Bloomberg 23jan03

Agent Orange, a defoliant the U.S. Army used in Vietnam to remove enemy forest cover, is linked to a form of leukemia, the U.S. Institute of Medicine said in a report that contradicts its earlier research.

A re-analysis of six studies showed that people exposed to the herbicide had an increased risk of chronic lymphocytic leukemia, or CLL, the most common form of the blood cancer in U.S. adults.

A number of other cancers and conditions, including bone cancer, nerve damage, and skin disorders, result from Agent Orange exposure. An earlier government report found no link between the chemical and a group of leukemias, and the institute asked a committee to re-examine the data with a focus on CLL.

"We're still trying to determine what this will mean for exposed veterans," said David Strogatz, an epidemiologist at the State University of New York at Albany who served on the IOM panel.

CLL is still a relatively rare cancer, striking about 7,000 each year in the U.S. In the studies the panel reviewed, people exposed to Agent Orange, mainly through farming and other rural occupations, had a risk of CLL 2 1/2 times greater than the general population.

"We would call this a modest association," Strogatz said. In comparison, long-time cigarette smoking raises the risk of cancer by about 10 times.

Since 1994, when the deadline expired to apply for compensation from a $180 million settlement fund, people exposed to Agent Orange have sued manufacturers including Dow Chemical Co. and Monsanto Co. The U.S. Supreme Court in November agreed to hear the companies' appeals that the settlement fund limited later suits.

Representatives for the companies didn't immediately return calls seeking comment.

Other defendants in the case include units of Occidental Petroleum Corp., Valero Energy Corp., YPF SA and Royal Philips Electronics NV.