Introduction Primary risk factors for urothelial carcinomas (UC) include smoking, occupational exposures to aromatic amines (AA) and polycyclic aromatic hydrocarbons (PAH). Radiation risk estimates of the A-bomb survivors indicate the bladder is highly radiosensitive. However, concerns persist as to whether high smoking rates or occupational exposures may have influenced these estimates. The purpose of this study is to re-estimate radiation risk estimates of UC while adjusting for smoking and occupational exposures to AAs and PAHs.

Methods A case-cohort study with stratified sampling of A-bomb survivors who completed a lifestyle survey. The sub-cohort consisted of 3195 persons sampled from an overall cohort of approximately 70 000 with an average age at entry of 52.7 years. There were 356 incident UCs between 1967 and 2001. Occupational exposures were assigned using a job exposure matrix from the US National Occupational Exposure Survey. An industrial hygienist assigned US Standard Industrial Classification codes (2-digit) based on questionnaires. Preliminary risk estimates were derived from Cox proportional hazards with robust estimates of variance.

Results The HR for 1 grey of radiation dose was 1.58 (95% CI 2.54 to 5.21). After adjusting for smoking and occupational exposures, the radiation HR was 1.49 (95% CI 1.01 to 2.18). The smoking HR was highly significant (2.86; 95% CI 2.00 to 4.09). No association was observed with occupational exposures.

Conclusions Results are preliminary. Improvements in variance estimation and the addition of occupational codes are still outstanding. However, these results indicate that previously reported risk estimates of UC are not largely biased by smoking or occupational exposures.