DO GAMMA-RAYS AND ALPHA-PARTICLES CAUSE DIFFERENT TYPES OF LUNG-CANCER - A COMPARISON BETWEEN ATOMIC-BOMB SURVIVORS AND URANIUM MINERS

Excess lung cancer risk has been associated with exposure to alpha par ticle radiation from inhaled radon daughter products among uranium min ers in Czechoslovakia, Canada, the United States, and elsewhere, and w ith exposure to gamma rays and neutrons from the atomic bombings of Hi roshima and Nagasaki, Japan. Differences in distribution by histologic al type, as well as certain epidemiological differences, suggest the p ossibility of differences in the causation of radiation-induced lung c ancer. An epidemiological analysis is summarised of results from a bli nd pathology panel review of tissue slides from lung cancer cases diag nosed in 108 Japanese A bomb survivors and 92 American uranium miners selected on the basis of radiation exposure, smoking history, sex, age , and source and quality of pathology material. Consensus diagnoses we re obtained with respect to principal sub-type, including squamous cel l cancer, small cell cancer, adenocarcinoma, and less frequent sub-typ es. The results were analysed in terms of population, radiation dose, and smoking history. As expected, the proportion of squamous cell canc er was positively related to smoking history in both populations. The relative frequencies of small cell cancer and adenocarcinoma were very different in the two populations, but this difference was adequately accounted for by differences in radiation dose (more specifically, dos e-based relative risk estimates based on published risk coefficients). Data for the two populations conformed to a common pattern, in which radiation-induced cancers appeared more likely to be of the small-cell sub-type, and less likely to be adenocarcinomas. No additional explan ation in terms of radiation quality (alpha particles or gamma rays), u niform or local irradiation, inhaled as against external radiation sou rce, or other population differences, appeared to be required. One pos sible interpretation of the finding is that radiation-related lung car cinogenesis may depend heavily on interactions with inhaled promoter/p rogressor agents, such as smoke. Thus, even though ionising events fro m external gamma rays and inhaled radon decay products are very differ ently distributed within the lung, the spatial distribution, and cell types, of any resulting cancers may be determined largely by the actio n of other agents deposited within the bronchi.