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News from the National Academies
Date: Sept. 1, 1998
Contacts: Molly Galvin, Media Relations Officer
Kristen Nye, Media Relations Assistant
(202) 334-2138; e-mail <news@nas.edu>

FOR IMMEDIATE RELEASE

Radiation From Bomb Tests Could Cause Thyroid Cancer,
But Screening Program Not Advisable

WASHINGTON -- Some Americans are at higher risk for developing thyroid cancer after being exposed to radioactive iodine released during nuclear bomb tests in the 1950s and 1960s, but the government should not sponsor national or regional thyroid cancer screening, says a new report by committees of the Institute of Medicine (IOM) and National Research Council. There is no evidence to suggest that early detection of thyroid cancer through a routine screening program would prolong lives or lead to other health benefits. Instead, the government should use resources to involve the public and the medical community in designing an information program about exposure to fallout, the risks of developing thyroid cancer, and potential benefits and drawbacks of testing for the disease.

"A national or regional screening effort could result in needless worry and unnecessary surgeries because the tests used to detect the disease are so often inconclusive," said IOM committee chair Robert Lawrence, associate dean for professional education and programs, Johns Hopkins School of Public Health, Baltimore. "Fortunately, the kind of thyroid cancer linked to radiation exposure is rarely fatal. This type of cancer can and should be detected and treated promptly during routine medical care. Rather than systematic screening, doctors and patients should decide jointly about testing for thyroid cancer."

Of people who are diagnosed with the kind of thyroid cancer linked to radiation, nine out of 10 live longer than 30 years after the cancer is found. Thyroid cancer in all forms accounts for less than 1 percent of total cancer deaths each year. No data indicate that a screening program would improve these survival rates, the report says.

To screen for thyroid cancer, doctors first search for lumps on the thyroid either by feeling the throat or performing ultrasound. Both methods are capable of locating several nodules since many adults in the general population have harmless, non-cancerous lumps on the thyroid. Because neither method detects cancer, tissue samples of the nodules would then be needed. Approximately 25 percent of these samples are indeterminate or unsatisfactory, and some are false-positive. Even some small nodules that are malignant will not grow or cause health problems. A national or regional screening program could result in many people being referred to unnecessary surgery, the report says. If all or part of the thyroid is removed, then a lifetime of hormone replacement therapy usually is required.

Concerns About Fallout

During the 1950s and 1960s, nearly 100 atmospheric nuclear bomb tests were conducted at a test site northwest of Las Vegas. One of the radioactive elements in the fallout from the tests was iodine-131, which concentrates in the thyroid gland when ingested or inhaled and has been linked to thyroid cancer. Approximately 160 million people living throughout the United States during the bomb tests might have been exposed to varying levels of iodine-131 for about two months following each test. However, iodine-131 has a radioactive half-life of about eight days, and the risk of harmful exposure decreased rapidly within days of each bomb test. Some people inhaled the radioactive iodine, but most were exposed indirectly through consuming milk from cows or goats that grazed on contaminated pasture land.

Prompted by public concern, Congress called for an assessment of potential exposure and related health risks, and in 1983 the federal National Cancer Institute (NCI) began a study. Last October, NCI released a report that estimated likely iodine-131 exposures across the nation. The IOM and the Research Council were each asked to appoint a committee. The IOM committee evaluated possible public health strategies to respond to exposure to the fallout, such as screening for thyroid cancer. The Research Council committee evaluated the methodology used in the NCI study, possible health consequences of exposure, and the NCI estimates of the number of thyroid cancers that might result. The new report presents the findings and conclusions of both committees.

Given that some 17,200 new cases of thyroid cancer are estimated to develop annually, about 1.2 million thyroid cancers will likely occur over a 70-year span. Accounting for uncertainties in measurements of fallout dispersed across the country and other factors such as the amount of milk people consumed at the time of the testing, NCI estimated that 11,300 to 212,000 additional thyroid cancers could develop over the decades as a result of the exposure to radioactive iodine.

After examining analyses of population data on thyroid cancer and mortality from several national cancer registries, the IOM and Research Council committees found little evidence of widespread increases in thyroid cancer related to the patterns of iodine-131 exposure described in the NCI report. The number of additional thyroid cancers is likely to be in the low end of NCI's estimated range, the report says. Moreover, almost half of the thyroid cancers resulting from this exposure already have appeared.

"NCI made an intensive effort to collect and generate data on events that occurred decades ago, and its estimates are scientifically based," said William Schull, Research Council committee chair and Ashbel Smith Professor Emeritus of the School of Public Health, University of Texas, Houston. "But the population data do not indicate increases in thyroid cancer that correspond to NCI's estimates of exposure across the nation. While data are too limited to calculate a precise number, the additional thyroid cancers that may result will probably be closer to the low end of NCI's estimates."

Estimates of Exposure

NCI based its estimates of radiation exposure on factors such as people's age at the time of the tests, where they lived, and what foods they consumed, particularly milk. Evidence suggests that childhood exposure to radioactive iodine -- especially before age 10 -- can increase the risk that a person will develop thyroid cancer at some point. Children who drank milk produced by cows or goats on family farms might have received higher than average exposure. This milk would have contained more iodine-131 than was present in commercially distributed milk, because it typically was consumed shortly after production, leaving little time for the radioactive iodine to decay. People who were teenagers or adults when the bomb tests were conducted, or who did not drink milk, are at very little risk of developing thyroid cancer from exposure to the fallout.

NCI's estimates of the amount of fallout that counties or states might have received are probably too imprecise to be used by individuals to determine their own exposure, the report says. Samples of the fallout were collected at fewer than 100 sites during the time of the tests, and these data are not sufficient to predict the amount of fallout across counties or states. Rather than estimating the average dose of iodine-131 that people might have received in each county, fallout data should be used for determining broad exposure levels over much larger regions of the United States.

Critical data needed to estimate an individual's risk of developing thyroid cancer often are unavailable or unreliable, the report says. Sound estimates of exposure should be based on the amount of milk consumed and whether the milk was produced by cows that grazed on contaminated pastures, but this information cannot usually be recalled or reconstructed accurately.

Communicating Risks

The U.S. Department of Health and Human Services -- responsible for communicating potential health risks from the bomb tests to the public -- should involve concerned citizens and the medical community to help develop information and materials, the report says. In addition, other groups should be consulted about their experiences in communicating about radiation risk -- such as the Centers for Disease Control and Prevention and the Hanford Health Information Network, which provides information to people who might have been exposed to iodine-131 and other radioactive materials released from a nuclear weapons facility in Hanford, Wash.

The federal government should consider the most effective methods for presenting risks and ways of distributing information to the public, the report says, such as establishing a resource center or providing material through the Internet or a toll-free number. Moreover, educational materials should be prepared for physicians, to guide discussions with patients who are concerned about thyroid cancer.

The study was funded by the U.S. Department of Health and Human Services. The National Research Council is the principal operating agency of the National Academy of Sciences and the National Academy of Engineering. It is a private, non-profit institution that provides science and technology advice under a congressional charter. The Institute of Medicine is a private, non-profit organization that provides health policy advice under the same charter. Rosters for each committee follow.

Read the full text of Exposure of the American People to Iodine-131 from Nevada Atomic Bomb Tests: Review of the National Cancer Institute Report and Public Health Implicationsfor free on the Web, as well as more than 1,800 other publications from the National Academies. Printed copies are available for purchase from the National Academy Press Web siteor at the mailing address in the letterhead; tel. (202) 334-3313 or 1-800-624-6242. Reporters may obtain a pre-publication copy from the Office of News and Public Information at the letterhead address (contacts listed above).


Institute of Medicine
Board on Health Care Services

Committee on Thyroid Screening Related to Iodine-131 Exposure

Robert S. Lawrence, M.D.(1)(chair)
Professor of Health Policy and Associate Dean for Professional Education and Programs
Johns Hopkins University
Baltimore

Catherine Borbas, Ph.D.
Executive Director
Healthcare Education and Research Foundation Inc.
St. Paul, Minn.

J. William Charboneau, M.D.
Professor of Radiology
Mayo Medical School, and
Staff Physician
Mayo Clinic Department of Radiology
Rochester, Minn.

Virginia A. LiVolsi, M.D.
Professor of Pathology, Department of Pathology and Laboratory Medicine
University of Pennsylvania School of Medicine
Philadelphia

Ernest L. Mazzaferri, M.D., M.A.C.P.
Professor and Chair, Department of Internal Medicine
Ohio State University
Columbus

Stephen G. Pauker, M.D.(1)
Vice Chairman for Clinical Affairs
New England Medical Center, and
Professor of Medicine
Tufts University
Boston


Henry Royal, M.D.
Associate Director, Division of Nuclear Medicine
Mallinckrodt Institute of Radiology
St. Louis


Samuel A. Wells Jr., M.D.(1)
Bixby Professor of Surgery and
Chairman, Department of Surgery
Washington University School of Medicine
St. Louis


Steven H. Woolf, M.D., M.P.H.
Professor of Family Medicine, Department of Family Practice
Medical College of Virginia
Fairfax


STAFF

Steven L. Simon
Study Director


NATIONAL RESEARCH COUNCIL
Commission on Life Sciences

Committee on Exposure of the American People to I-131 from the Nevada Atomic Bombs Tests

William J. Schull, Ph.D.(chair)
Ashbel Smith Professor Emeritus
School of Public Health
University of Texas
Houston

Keith Baverstock, Ph.D.
Director, Radiation Protection Programme
World Health Organization, European Centre for Environment and Health
Rome

Stephen Benjamin, D.V.M., Ph.D.
Professor, Department of Pathology, Radiological Health Sciences, and Environmental Health
College of Veterinary Medicine and Biomedical Sciences
Colorado State University
Fort Collins

Patricia Buffler, Ph.D.(1)
Dean and Professor of Epidemiology
School of Public Health
University of California
Berkeley

Sharon Dunwoody, Ph.D.
Evjue-Bascom Professor of Journalism and Mass Communication
University of Wisconsin
Madison

Peter Groer, Ph.D.
Associate Professor, Department of Nuclear Engineering
University of Tennessee
Knoxville

Robert Lawrence, M.D.(1)
Associate Dean of Professional Education and Programs and Professor of Health Policy
Johns Hopkins University
Baltimore

Carl Mansfield, M.D.
Chairman of the Radiation Oncology Department
University of Maryland Medical Systems
Baltimore

James Martin, Ph.D.
Associate Professor of Radiological Health
University of Michigan
Ann Arbor
Ernest Mazzaferri, M.D.
Professor and Chair, Department of Internal Medicine
Ohio State University
Columbus

Kathryn Merriam, Ph.D.
Owner and President
Synthesis Inc. and Project Turnaround
Pocatello, Idaho

Dade Moeller, Ph.D.(2)
President
Dade Moeller & Associates Inc.
New Bern, N.C.

Christopher Nelson, B.S.
Environmental Engineer
Office of Radiation and Indoor Air
Environmental Protection Agency
Washington, D.C.

Henry Royal, M.D.
Associate Director, Division of Nuclear Medicine
Mallinckrodt Institute of Radiology
St. Louis

Richard H. Schultz, M.S.
Administrator
Idaho State Division of Health
Department of Health and Welfare
Boise

Daniel Stram, Ph.D.
Associate Professor, Department of Preventative Medicine
University of Southern California
Los Angeles

Robert G. Thomas, Ph.D.
Consultant
Kallispell, Mont.

STAFF

Marilyn J. Field, Ph.D.
Study Director

(1) Member, Institute of Medicine
(2) Member, National Academy of Engineering