Breast cancer incidence at a nuclear facility: demonstration of a morbidity surveillance system

In order to provide a timely means of identifying new or unexpected toxicities which may occur as a result of occupational exposures, the United States Department of Energy is currently developing a system of routine morbidity surveillance at selected nuclear facilities. Examination of surveillance data at the Hanford Site identified a possible increase in breast cancer incidence (based on three observed cases) among women working in the nuclear trades compared to all other women at the site (relative risk = 3.1; exact 95% confidence interval = 0.7-9.7). This triggered a more detailed investigation using a nested case-control design and individual dosimetry readings. Information on nineteen breast cancer cases occurring at the site between 1984 and 1989 and 71 matched controls were abstracted from existing occupational medicine, administrative, and health physics records. Summary variables for cumulative, average, and peak external radiation dose equivalents were calculated after allowing for 1 y and 10 y induction and latency periods. There was no evidence that the observed excess was due to radiation exposure. Since the surveillance system is designed to be ongoing, continued monitoring of breast cancer rates in this occupational group will be carried out, and more appropriately detailed studies begun if consistently elevated rates are observed.