July 6, 2006

Higher thyroid cancer rate from Chernobyl confirmed

NEW YORK (Reuters Health) - A new study confirms a
substantially increased risk of thyroid cancer among people
exposed to radiation during childhood and adolescence after the
1986 Chernobyl nuclear accident.

A total of 13,127 of the 32,385 individuals living in the
most contaminated area of the Ukraine during the nuclear plant
meltdown and who were under 18 at the time were screened
between 1998 and 2000, Dr. Geoffrey R. Howe of Columbia
University in New York and colleagues report. They found that
45 cases of thyroid cancer occurred compared with 11.2 cases
that would have been expected in the absence of radiation
exposure. Plus, the higher the dosage of radioactive iodine,
the greater the thyroid cancer risk.

The study is the first to measure the risk of thyroid
cancer associated with specific radiation dosage, Howe and his
team note in the Journal of the National Cancer Institute.
Radioactive iodine and cesium were the main components of the
Chernobyl fallout. Because radioactive iodine is used
frequently in medicine -- and is also likely to be a chief
contaminant released in any future nuclear emergency --
understanding the risk associated with exposure is a public
health concern, as well as of scientific interest, the
researchers point out.

A spike in thyroid cancer cases had already been observed
among Ukraine residents who were children and adolescents when
the Chernobyl accident occurred. However, the researchers note,
increased rates of screening for thyroid cancer and a low
dietary iodine intake, which increases the uptake of
radioactive iodine by the thyroid gland, "almost certainly"
were factors in this increase.

To investigate the specific risk associated with radiation
exposure, the researchers estimated each person's radiation
exposure using measurements made after the accident and from

They found a "strong" relationship between radiation
exposure and thyroid cancer risk. While there was a tendency
for risk to be greater among people exposed at younger ages, as
well as among females, neither was statistically significant.

"We estimate that 75 percent of the thyroid cancer cases
would have been avoided in the absence of radiation," the
researchers conclude. "This estimate demonstrates a substantial
contribution of radioactive iodines to the excess of thyroid
cancer that followed the Chernobyl accident."

SOURCE: Journal of the National Cancer Institute, July 5,