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Hormone replacement therapy in relation to breast carcinoma incidence rate ratios
A prospective Danish cohort study
Article first published online: 23 APR 2004
Copyright © 2004 American Cancer Society
Volume 100, Issue 11, pages 2328–2337, 1 June 2004
How to Cite
Tjønneland, A., Christensen, J., Thomsen, B. L., Olsen, A., Overvad, K., Ewertz, M. and Mellemkjær, L. (2004), Hormone replacement therapy in relation to breast carcinoma incidence rate ratios. Cancer, 100: 2328–2337. doi: 10.1002/cncr.20250
- Issue published online: 18 MAY 2004
- Article first published online: 23 APR 2004
- Manuscript Accepted: 3 MAR 2004
- Manuscript Revised: 26 FEB 2004
- Manuscript Received: 18 DEC 2003
- Danish Cancer Society
- Europe Against Cancer program (European Prospective Investigation into Cancer and Nutrition [EPIC] project)
- hormone replacement therapy;
- estrogen receptor status;
- postmenopausal breast carcinoma;
- lobular carcinoma
The goal of the current study was to investigate the relation between hormone replacement therapy (HRT) and breast carcinoma in a prospective study cohort. Particular attention was paid to the type of HRT used and to the association of HRT type with estrogen receptor status and tumor histology.
Between 1993 and 1997, a total of 29,875 women were enrolled in the Danish Cancer Society's prospective “Diet, Cancer and Health” study. Among 23,618 women who were assumed to be postmenopausal and for whom information on HRT use was available, we identified 423 cases of breast carcinoma over a median follow-up period of 4.8 years. Statistical analyses were based on the Cox proportional hazards model, with age serving as the time parameter.
The breast carcinoma incidence rate ratio (IRR) was 2.22 (95% confidence interval [CI], 1.80–2.75) for users of HRT at baseline compared with women who never received HRT. Among HRT users (relative to nonusers), the IRR for estrogen receptor–positive tumors (2.38; 95% CI, 1.84–3.06) was greater than the IRR for estrogen receptor–negative tumors (1.56; 95% CI, 1.00–2.43). HRT use at baseline also was analyzed in relation to the incidence of lobular carcinoma and the incidence of ductal carcinoma; the adjusted IRR associated with HRT use was 3.53 (95% CI, 1.94–6.41) for lobular carcinoma and 2.10 (95% CI, 1.64–2.70) for ductal carcinoma. The likelihood of developing estrogen receptor–positive breast carcinoma was found to depend significantly on the type of HRT regimen used (P = 0.03), with women receiving continuous therapy having the greatest probability of developing estrogen receptor–positive disease.
An increased breast carcinoma IRR was found to be associated with current HRT use. In addition, relative to other types of HRT regimens, continuous estrogen + progestin regimens were found to be associated with an increased risk of breast carcinoma, and particularly estrogen receptor–positive breast carcinoma. Cancer 2004. © 2004 American Cancer Society.