Abstract
The Radiation Effects Research Foundation has conducted a mortality study since 1950 and a cancer incidence study since 1958 on a fixed population (LSS cohort) of about 120,000 subjects including atomic-bomb survivors and their controls to determine health effects of atomic-bomb radiation. Clinical examinations have also been conducted biennially for about 20% of the LSS cohort since 1958.
The most important late effect observed among atomic-bomb survivors is an increase of cancer risk. In contrast to the leukemia risk, the risk of solid cancers (stomach, lung, etc.) started increasing only after the exposed reached the cancer-prone age, and now continues to increase in proportion to the increase of the background cancer risk.
We have studied whether radiation risk on solid cancers varies depending on the site, radiation dose, sex, age, or the state of exposure to other carcinogens, including cigarettes. In summary, although no statistically significant increase in cancer risk has been observed for some sites, including the rectum and pancreas, an effect from radiation has been observed for the cancers of many sites, including the lung, stomach, and colon. The dose-response relationship for these sites shows a linear increase with radiation dose. The younger was the age at exposure, the higher the relative risk. The effect of radiation does not vary significantly by other carcinogenic factors, including smoking.
With the elapse of 60 years after the atomic bombings, the proportion of living subjects of the LSS cohort has decreased to 50% or under. About 80% of those exposed before age 20 are still alive. The mortality and cancer incidence studies for the LSS cohort will continue to provide important information.
