Towards an integrated model for breast cancer etiology: The crucial role of the number of mammary tissue-specific stem cells

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Abstract

Perinatal events and conditions, notably birth weight, are associated with breast cancer risk in offspring, and correlates of mammary gland mass are predictors of breast cancer risk. These findings may be interpreted as indicating that high levels of estrogens and components of the insulin-like growth factor system during pregnancy favour the generation of mammary tissue-specific stem cells, and that the number of these cells, which is positively associated with mammary gland mass, is an important determinant of breast cancer risk. Perinatal events and conditions may also affect risk for other malignancies, but the evidence in the case of breast cancer is prominent, possibly because estrogens and the insulin-like growth factor system are both involved in breast cancer etiology and affect birth weight.

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Breast cancer and hormone-replacement therapy in the Million Women Study.

Valerie Beral (2003)

Current use of hormone-replacement therapy (HRT) increases the incidence of breast cancer. The Million Women Study was set up to investigate the effects of specific types of HRT on incident and fatal breast cancer. 1084110 UK women aged 50-64 years were recruited into the Million Women Study between 1996 and 2001, provided information about their use of HRT and other personal details, and were followed up for cancer incidence and death. Half the women had used HRT; 9364 incident invasive breast cancers and 637 breast cancer deaths were registered after an average of 2.6 and 4.1 years of follow-up, respectively. Current users of HRT at recruitment were more likely than never users to develop breast cancer (adjusted relative risk 1.66 [95% CI 1.58-1.75], p<0.0001) and die from it (1.22 [1.00-1.48], p=0.05). Past users of HRT were, however, not at an increased risk of incident or fatal disease (1.01 [0.94-1.09] and 1.05 [0.82-1.34], respectively). Incidence was significantly increased for current users of preparations containing oestrogen only (1.30 [1.21-1.40], p<0.0001), oestrogen-progestagen (2.00 [1.88-2.12], p<0.0001), and tibolone (1.45 [1.25-1.68], p<0.0001), but the magnitude of the associated risk was substantially greater for oestrogen-progestagen than for other types of HRT (p<0.0001). Results varied little between specific oestrogens and progestagens or their doses; or between continuous and sequential regimens. The relative risks were significantly increased separately for oral, transdermal, and implanted oestrogen-only formulations (1.32 [1.21-1.45]; 1.24 [1.11-1.39]; and 1.65 [1.26-2.16], respectively; all p<0.0001). In current users of each type of HRT the risk of breast cancer increased with increasing total duration of use. 10 years' use of HRT is estimated to result in five (95% CI 3-7) additional breast cancers per 1000 users of oestrogen-only preparations and 19 (15-23) additional cancers per 1000 users of oestrogen-progestagen combinations. Use of HRT by women aged 50-64 years in the UK over the past decade has resulted in an estimated 20000 extra breast cancers, 15000 associated with oestrogen-progestagen; the extra deaths cannot yet be reliably estimated. Current use of HRT is associated with an increased risk of incident and fatal breast cancer; the effect is substantially greater for oestrogen-progestagen combinations than for other types of HRT.

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Endogenous sex hormones and breast cancer in postmenopausal women: reanalysis of nine prospective studies.

T Key, P Appleby, I. Barnes … (2002)

Reproductive and hormonal factors are involved in the etiology of breast cancer, but there are only a few prospective studies on endogenous sex hormone levels and breast cancer risk. We reanalyzed the worldwide data from prospective studies to examine the relationship between the levels of endogenous sex hormones and breast cancer risk in postmenopausal women. We analyzed the individual data from nine prospective studies on 663 women who developed breast cancer and 1765 women who did not. None of the women was taking exogenous sex hormones when their blood was collected to determine hormone levels. The relative risks (RRs) for breast cancer associated with increasing hormone concentrations were estimated by conditional logistic regression on case-control sets matched within each study. Linear trends and heterogeneity of RRs were assessed by two-sided tests or chi-square tests, as appropriate. The risk for breast cancer increased statistically significantly with increasing concentrations of all sex hormones examined: total estradiol, free estradiol, non-sex hormone-binding globulin (SHBG)-bound estradiol (which comprises free and albumin-bound estradiol), estrone, estrone sulfate, androstenedione, dehydroepiandrosterone, dehydroepiandrosterone sulfate, and testosterone. The RRs for women with increasing quintiles of estradiol concentrations, relative to the lowest quintile, were 1.42 (95% confidence interval [CI] = 1.04 to 1.95), 1.21 (95% CI = 0.89 to 1.66), 1.80 (95% CI = 1.33 to 2.43), and 2.00 (95% CI = 1.47 to 2.71; P(trend)<.001); the RRs for women with increasing quintiles of free estradiol were 1.38 (95% CI = 0.94 to 2.03), 1.84 (95% CI = 1.24 to 2.74), 2.24 (95% CI = 1.53 to 3.27), and 2.58 (95% CI = 1.76 to 3.78; P(trend)<.001). The magnitudes of risk associated with the other estrogens and with the androgens were similar. SHBG was associated with a decrease in breast cancer risk (P(trend) =.041). The increases in risk associated with increased levels of all sex hormones remained after subjects who were diagnosed with breast cancer within 2 years of blood collection were excluded from the analysis. Levels of endogenous sex hormones are strongly associated with breast cancer risk in postmenopausal women.

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Influence of estrogen plus progestin on breast cancer and mammography in healthy postmenopausal women: the Women's Health Initiative Randomized Trial.

Rowan Chlebowski, Susan L Hendrix, Robert D. Langer … (2003)

The Women's Health Initiative trial of combined estrogen plus progestin was stopped early when overall health risks, including invasive breast cancer, exceeded benefits. Outstanding issues not previously addressed include characteristics of breast cancers observed among women using hormones and whether diagnosis may be influenced by hormone effects on mammography. To determine the relationship among estrogen plus progestin use, breast cancer characteristics, and mammography recommendations. Following a comprehensive breast cancer risk assessment, 16 608 postmenopausal women aged 50 to 79 years with an intact uterus were randomly assigned to receive combined conjugated equine estrogens (0.625 mg/d) plus medroxyprogesterone acetate (2.5 mg/d) or placebo from 1993 to 1998 at 40 clinical centers. Screening mammography and clinical breast examinations were performed at baseline and yearly thereafter. Breast cancer number and characteristics, and frequency of abnormal mammograms by estrogen plus progestin exposure. In intent-to-treat analyses, estrogen plus progestin increased total (245 vs 185 cases; hazard ratio [HR], 1.24; weighted P<.001) and invasive (199 vs 150 cases; HR, 1.24; weighted P =.003) breast cancers compared with placebo. The invasive breast cancers diagnosed in the estrogen plus progestin group were similar in histology and grade but were larger (mean [SD], 1.7 cm [1.1] vs 1.5 cm [0.9], respectively; P =.04) and were at more advanced stage (regional/metastatic 25.4% vs 16.0%, respectively; P =.04) compared with those diagnosed in the placebo group. After 1 year, the percentage of women with abnormal mammograms was substantially greater in the estrogen plus progestin group (716 [9.4%] of 7656) compared with placebo group (398 [5.4%] of 7310; P<.001), a pattern which continued for the study duration. Relatively short-term combined estrogen plus progestin use increases incident breast cancers, which are diagnosed at a more advanced stage compared with placebo use, and also substantially increases the percentage of women with abnormal mammograms. These results suggest estrogen plus progestin may stimulate breast cancer growth and hinder breast cancer diagnosis.

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Author and article information

Journal

Journal ID (nlm-ta): Breast Cancer Res

Title: Breast Cancer Research

Publisher: BioMed Central (London )

ISSN (Print): 1465-5411

ISSN (Electronic): 1465-542X

Publication date (Print): 2005

Publication date (Electronic): 5 November 2004

Volume: 7

Issue: 1

Pages: 13-17

Affiliations

[1 ]Department of Epidemiology, Harvard School of Public Health, Boston, Massachusetts, USA

[2 ]Department of Hygiene and Epidemiology, School of Medicine, University of Athens, Athens, Greece

[3 ]Department of Medical Epidemiology and Biostatistics, Karolinska Institutet, Stockholm, Sweden

Article

Publisher ID: bcr966

DOI: 10.1186/bcr966

PMC ID: 1064112

PubMed ID: 15642176

SO-VID: d412e42f-ca65-4071-ace4-9a5364837985

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