Cancer incidence among large cohort of female Danish registered nurses.

BACKGROUND: Nurses are potentially exposed to carcinogens in their working environment. We investigated the risks for 21 types of cancers in Danish nurses.
METHODS: We identified 92 140 female nurses from the computerized files of the Danish Nurses' Association. By record linkage, we reconstructed information on employment since 1964 using data from a national pension fund; information on vital status and reproduction was obtained from the Central Population Register. Each woman was followed-up from 1980-2003 in the Danish Cancer Registry. We calculated standardized incidence ratios (SIR) and 95% confidence intervals (95% CI). Using Poisson regression models, we made internal comparisons in subgroups of nurses, adjusting for potential confounders.
RESULTS: We documented 8410 cancers during follow-up and found significantly increased SIR for breast cancer (SIR 1.1, 95% CI 1.1-1.2), cancers of the brain and nervous system (SIR 1.2, 95% CI 1.1-1.3), melanoma (SIR 1.2, 95% CI 1.1-1.3), and other skin cancers (SIR 1.2, 95% CI 1.1-1.2). Significantly decreased risks were observed for alcohol- and tobacco-related cancers. Nurses who were accredited by the Association after 1981 had significantly increased risks for thyroid cancer (SIR 1.9, 95% CI 1.3-2.5) and cancers of the brain and nervous system (SIR 1.5, 95% CI 1.2-1.9). Former nurses had significantly increased SIR for all cancers combined and breast cancer the first ten years after leaving the profession. In a Poisson regression analysis of breast cancer and duration of employment in hospitals, adjusted for reproductive factors, nurses had an increase risk the first 25 years of employment, but not for longer periods.
CONCLUSION: The increased risk of breast cancer and the decreased risk of alcohol- and tobacco-related cancers support the findings of most other studies on nurses. The elevated risks for cancers of the breast, brain, nervous system, and thyroid warrant further study.