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Posted on 10-24-2010

Hormone Replacement Therapy and Risk of Breast Cancer With a Favorable Histology

Results of the Iowa Women's Health Study

Susan M. Gapstur, PhD; Monica Morrow, MD; Thomas A. Sellers, PhD

JAMA. 1999;281:2091-2097.

Context  Long-term, postmenopausal use of hormone replacement therapy (HRT) appears to increase breast cancer risk. Whether the effect of HRT use on risk of breast cancer varies among histological types of invasive carcinoma is unknown.

Results  Duration of ever HRT use was associated with risk of invasive carcinoma with a favorable histology, with an RR of 1.81 (95% confidence interval [CI], 1.07-3.07) for thosewho used HRT 5 or fewer years vs an RR of 2.65 (95% CI, 1.34-5.23) for those who used HRT for more than 5 years (P for trend=.005) after adjustment for age and other breast cancer risk factors. There was no association between ever HRT use and the incidence of DCIS or invasive ductal or lobular carcinoma. Among current hormone users, after adjusting for age and other breast cancer risk factors, the RRs (95% CIs) of invasive carcinoma with a favorable histology were 4.42 (2.00-9.76) and 2.63 (1.18-5.89) for 5 or fewer years of use and for more than 5 years of use, respectively. Risk of invasive ductal or lobular carcinoma was associated with current use (5 years) of HRT with an RR of 1.38 (95% CI, 1.03-1.85).

Conclusions  Exposure to HRT was associated most strongly with an increased risk of invasive breast cancer with a favorable prognosis. These data add important clinical information for assessing the risks and benefits of HRT use.

Author Affiliations: Departments of Preventive Medicine (Dr Gapstur) and Surgery (Dr Morrow), and Lynn Sage Comprehensive Breast Center (Dr Morrow), Northwestern University Medical School, Chicago, Ill; and Department of Health Sciences Research, Mayo Clinic/Foundation, Rochester, Minn (Dr Sellers).

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