The rate of thyroid cancer in a region north of the Chernobyl nuclear plant is nearly 200 times higher than normal, according to research published in the British Medical Journal.
Scientists from Russia, Ukraine, Belarus and the World Health Organization said abnormally high rates of thyroid cancer in children had also been detected farther away in the northern Ukraine and parts of Russia.
The cancer has appeared most in children because they are more sensitive to radiation and their thyroid glands are smaller, so a given amount of radiation represents a larger dose than for an adult.
In their letter to the journal, the scientists said some of the exposure probably came from contaminated milk.
In Gomel, a city in Belarus 70 miles north of Chernobyl, 143 cases of thyroid cancer were diagnosed between 1991 and 1994 in children under 15, the scientists said. That was a rate of 96.4 per million, compared to the normal rate of 0.5 per million.
In Belarus as a whole, the rate of thyroid cancer in children was 30.6 per million, the researchers said, with more than 330 cases reported since 1986.
The increase in thyroid cancer is linked to fallout of radioactive iodine, which concentrates in the thyroid gland.
Higher rates of thyroid cancer in children have been noted for some time following the April 1986 explosion. From 1986 to 1990, 21 cases were reported in Gomel - a rate of 10.5 per million, or 21 times the expected rate, according to the letter in the journal.