Reevaluation of lung cancer risk in the acrylonitrile cohort study of the National Cancer Institute and the National Institute for Occupational Safety and Health

Objectives The present study provides additional analyses of data obtained earlier on lung cancer risk among workers with acrylonitrile exposure. Methods The original authors provided the data. For total mortality and the cancer sites of a priori interest (lung, stomach, brain, breast, prostate, and the lymphatic and hematopoietic systems), standardized mortality ratio s (SMR) and 95% confidence intervals (95% CI) were computed, the total Unit ed States and surrounding counties being used as standard populations. Regi onal rate-based SMR values were also computed between lung cancer and cumul ative acrylonitrile exposure. Results Except for lung cancer, the external comparisons corroborated the e arlier internal comparisons (no increased cancer mortality risk). For lung cancer, the external comparisons revealed death deficits for the unexposed workers (SMR 0.68, 95% CI 0.5-0.9) and all categories of acrylonitrile-expo sed workers. The SMR obtained using external rates and the most exposed gro up (SMR 0.92, 95% CI 0.6-1.4) differed from the corresponding relative risk (RR) of the internal rates (RR 1.5, 95% CI 0.9-2.4). Conclusions The analysis of the present study provides little evidence that acrylonitrile exposure increases the mortality risk of cancers of a priori interest, including lung cancer. The lung cancer findings of the external comparison differed from the earlier findings of the internal comparisons. Selection bias (as the healthy worker effect) was probably not responsible. Additional follow-up and analyses, especially of the unexposed workers wit h low lung cancer rates, may help elucidate the internal and external compa rison differences. Results from both comparisons should be presented when t he relative risks differ markedly, as both have advantages and disadvantage s.