1. ¹Channing Laboratory, Department of Medicine, Brigham and Women's Hospital and Harvard Medical School, Boston, MA, USA
2. ²Department of Epidemiology, Harvard School of Public Health, Boston, MA, USA
3. ³Department of Pathology, Beth-Israel Deaconess Medical Center, Boston, MA, USA
4. ⁴Department of Biostatistics, Harvard School of Public Health, Boston, MA, USA

Correspondence: Dr KN Danforth, Channing Laboratory, 181 Longwood Avenue, 3rd Floor, Boston, MA 02115, USA. E-mail: kim.danforth@channing.harvard.edu

Received 3 July 2006; Revised 13 November 2006; Accepted 15 November 2006; Published online 19 December 2006.

Abstract

The relationship between postmenopausal hormone use (PMH) and ovarian cancer risk is unclear, particularly for specific hormone formulations, but recent studies suggest that there is a positive association. We conducted a prospective observational study with 82 905 postmenopausal women, including 389 ovarian cancers, in the Nurses' Health Study from 1976 to 2002. Compared with never users of PMH, both current and past users of 5 years had a significantly elevated risk of ovarian cancer (RR=1.41, 95% confidence interval (CI) 1.07–1.86 and relative risk (RR)=1.52, 95% CI 1.01–2.27, respectively). Examined by hormone type in continuous years, use of unopposed estrogen was associated with a significant increase in the risk of epithelial ovarian cancer (P for trend <0.001; RR for 5-year increment of use=1.25, 95% CI 1.12–1.38). Use of estrogen plus progestin (RR for 5-year increment of use=1.04, 95% CI 0.82–1.32) was not significantly associated with ovarian cancer risk. Generally, results were similar for serous tumours (RR for 5-year increment of unopposed estrogen use=1.23, 95% CI 1.07–1.40) and slightly stronger for endometrioid tumours (RR for 5-year increment of unopposed estrogen use=1.53, 95% CI 1.20–1.94). Recency of use was not significantly associated with ovarian cancer risk, but statistical power was limited here.