Nearly 2000 cases of thyroid cancer have been linked to the world's worst nuclear accident which occurred in Ukrainian city 15 years ago - and the number is still rising.
Professor Dillwyn Williams, of The Strangeways Research Laboratory, Cambridge University, told the meeting: "Four years after the accident, an excess of thyroid cancers was noted among children who had been exposed to fall-out from the disaster. That increase has continued and new cases are still being seen in those who were children at the time of the accident".
Dr. Elaine Ron, of the US National Cancer Institute, in Bethesda, Maryland, explained: "Following external radiation exposure, the elevated risk of thyroid cancer appears to continue throughout life, but there is some indication that the risk may be highest 15 to 19 years after exposure.
External radiation is the only well established cause of cancer of the thyroid gland. People under 20 are at a significantly increased risk of thyroid cancer after exposure to isotopes of iodine. It is estimated that in the accident, the Chernobyl-4 reactor released all of the xenon gas, about half of the iodine and caesium and about three to five per cent of the remaining radioactive material.
Professor Williams said: "Exposure to isotopes of iodine gives the thyroid over a 1000 times the average dose to the rest of the body. The particular sensitivity of children to thyoid cancer after radiation exposure can be linked to a combination of a higher thyroid dose and the biology of thyroid growth - which falls to a very low level in adult life. Few of the patients with thyroid cancer have died, but help is still needed".
The UN recently marked the 15th anniversary of the disaster with an appeal for aid. According to one report, five million people in the former Soviet Union were exposed to radiation or other health hazards by the Chernobyl catastrophe. Although only 31 people died in the immediate aftermath of the accident, hundreds of thousands were reported to have abandoned entire cities and settlements within the 30 kilometre zone of extreme contamination.
Dr. Williams said: "The effects of Chernobyl differed very greatly from those after the atomic bomb explosions. In Japan, the exposure was very largely to whole body radiation from gamma rays and neutrons. After Chernobyl the exposure was to isotopes in fall-out, and apart from the inert gas xenon, the largest components were radioactive isotopes of iodine".
Post Chernobyl cancer risks are not restricted to the thyroid gland the meeting was told. Mr. Victor Chizhikov, of the Cancer Research Center, Kashirskoye, Moscow, reported that a study of former 43 Chernobyl "clean-up" workers had shown them to be at a significantly increased risk of lung cancer. Comprising 36 smokers and seven non-smokers, they all had evidence of inhaled radioactive dust in their lungs. They were compared to a control group of 21 smokers and 23 non-smokers who had never been exposed to radiation.
Abstract Nos. Professor Williams (498); Dr. Ron (497); Mr. Chizhikov (558).
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