Risk of Endometriosis and Subsequent Ovary and Breast Cancers in Nurses: A Population-Based Cohort Study in Taiwan

Abstract

Background: Endometriosis has been associated with the subsequent development of ovarian and breast cancers. This study evaluated whether nurses were at increased risks of developing endometriosis and subsequent ovarian and breast cancers. Methods: From Taiwan National Health Insurance Research Database during 2000 to 2011, we established 3 study cohorts, consisting of 23,801 nurses, 11,973 other hospital employees, and 143,096 general women free of endometriosis and cancer. Women in all cohorts were followed to the end of 2011 to measure the occurrences of endometriosis and subsequent ovarian and breast cancers. The incident endometriosis cases and related hazard ratio (HR) and 95% confidence interval (CI) were calculated. The incident cases of ovarian cancer and breast cancer and related odds ratio were calculated. Results: The incidence of endometriosis was the highest in the nurse cohort (4.23 per 100, n = 966) followed by other health professionals (3.74 per 100, n = 427) and control cohort (3.06 per 100, n = 4193), with adjusted hazard ratios of 1.28 (95% CI = 1.20–1.38) and 1.13 (95% CI = 1.02–1.25), respectively, comparing to controls. Among those who developed endometriosis, nurses had higher subsequent ovarian cancer and lower breast cancer, but not significant. Conclusions: Nurses are at a higher risk of developing endometriosis. However, the link between endometriosis and subsequent cancers is weak.