Estrogen, estrogen plus progestin therapy, and risk of breast cancer

Channing Laboratory, Department of Medicine, Brigham and Women's Hospital, and Harvard Medical School, Boston, MA 02115. USA.
Clinical Cancer Research (Impact Factor: 8.72). 02/2005; 11(2 Pt 2):909s-17s.
Source: PubMed


Epidemiologic evidence relating use of postmenopausal hormones to risk of breast cancer by nature relies on trends in prescribing practices. Data on the adverse effect of combination estrogen plus progestin used for long durations has only become available over the past decade. Evidence is reviewed relating estrogen alone and estrogen plus progestin to increased risk of breast cancer. Whereas current evidence indicates that longer duration of use increases risk of invasive breast cancer regardless of formulation, the rate of increase in risk is greater for combination estrogen plus progestin therapy. Although data are limited, continuous combined therapy and sequential therapy seem to have comparable impact on breast cancer risk. Combination therapy is more strongly related to lobular breast cancer than is estrogen alone. Unresolved issues remain about dose of estrogen and progestin in relation to risk, and about identification of women for whom short-term use to relieve menopausal symptoms may be safe and effective.

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    • "The model could also be improved by including combined HRT and the additional effect of progestin on breast cancer risk. Although combined HRT has a greater effect on breast cancer risk than estrogen-only HRT, the same patterns of interaction with BMI have been observed for both types of HRT [32]. Finally, the model could be refined to reflect the greater effect of estradiol on estrogen-receptor positive than estrogen-receptor negative breast cancer [33]. "
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    • "Studies of blood estrogen levels among postmenopausal women have shown that higher levels are associated with increased risk of subsequent breast cancer (Colditz 1998; Friel, Hinchcliffe, and Wright 2005; Key et al. 2002). The Million Women Study (MWS) showed a significant increase in the RR of breast cancer in women taking estrogens (conjugated equine estrogens or estradiol orally) (Relative Risk ¼ 1.30), although the increase was greater for women taking estrogens combined with synthetic progestins (RR ¼ 2.00) (Beral 2003). "
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