Cancer identification using a tumor registry versus death certificates in occupational cohort studies in the United States.

Studies of cancer incidences among occupational cohorts are rarely performed in the United States because of incomplete registration and a limited time period available for follow-up. This study used data from concurrent studies of cancer mortality and incidence among a cohort of 4,528 fire fighters and police officers employed by the cities of Seattle and Tacoma, Washington, between 1944 and 1979 to examine the relative advantages of tumor registry and death certificate information. As expected, an increased ability to study relatively common cancers with low fatality rates was demonstrated using incidence data. The most dramatic example was seen for bladder cancer. Twenty-four bladder cancers had been diagnosed among the study cohort between 1974 and 1989, whereas only two deaths were attributed to this malignancy. The standardized incidence ratio for bladder cancer was 1.05 (95% confidence interval 0.67-1.55), whereas the corresponding standardized mortality ratio was 0.46 (95% confidence interval 0.05-1.65). The observed relative risk estimates for rapidly fatal cancers were similar using the two sources of information, and no increase in precision was observed. Of 142 persons in the registry area who died of cancer during the study period, 20 (14%) had a different site listed on the death certificate than was identified by the registry. Approximately 7% of the potential person-years of follow-up were lost due to migration out of the registry area; loss to follow-up was greater among older and short-term workers, but did not exceed 13% of the person-years. Population-based tumor registries can be a useful resource in the investigation of occupational cancer in the United States, especially for the study of cancers with high survival rates.