[Radiation-induced cancers following radiotherapy of benign diseases: the second mail survey in Japan]

On a second mail survey (in 1984) concerning radiation-induced cancer following radiotherapy for benign diseases, 86 cases were collected from 95 hospitals in Japan. Adding these to 150 cases collected in the previous survey in 1979, 236 cases were accumulated. This is a report on the analysis of the 236 cases from a clinicopathological viewpoint. Underlying diseases consisted of cervical tuberculous lymphadenitis (125 cases), skin diseases (41 cases), benign thyroid diseases (19 cases), hemangioma (18 cases) and others (33 cases). Radiation-induced cancers, which were defined as cancers originating in the radiation field, including leukemia, consisted of hypopharyngeal cancer (68 cases), skin cancer (61 cases), laryngeal cancer (26 cases), esophageal cancer (23 cases), thyroid cancer (23 cases), salivary gland tumor (8 cases) and others (27 cases). Multiple primary cancers in the radiation field were observed in 7 cases. Average latent period was 28.9 years. It was demonstrated that the older the age at irradiation the shorter the latent period. Based on the population irradiated for benign diseases before 1977, which was collected in the first mail survey, incidence of radiation-induced cancers was estimated to be about 0.9%. The incidence varied with the period of radiotherapy; 1.9% for the period of radiotherapy before 1955, 0.4% for 1956-1965, 0.1% for 1966-1977. Although radiotherapy is now rarely indicated for benign diseases, it was shown in the first mail survey that more than 15,000 cases of benign diseases had been irradiated after 1956. It seems to be reasonable to consider that radiation-induced cancers after radiotherapy for benign diseases may continue to be discovered for several years in the future.