This document summarizes 15 peer-reviewed studies on the relationships between hormone therapy and breast cancer risk. The studies examined factors like joint estrogen and progesterone receptor status, marital status, reproductive behaviors, discontinuation of hormone therapy, and types of hormonal contraceptives. Overall, the studies presented varying and sometimes conflicting findings on the impacts of hormones on breast cancer risk.

1. Ma H, Bernstein L, Pike M, Ursin G. Reproductive factors and breast cancer risk according to joint estrogen and progesterone receptor status: a meta-analysis of epidemiological studies. Breast Cancer Research. 8(4), 2006.
Langer R. The evidence base for HRT: what can we believe? Climacteric. 20(2), 2017.
Fraumeni JF. Cancer mortality among nuns: role of marital status in etiology of neoplastic disease in women. J Natl Cancer Inst. 1969;42: 455–468.
Clark J. A critique of the Women’s Health Initiative Studies (2002-2006). Nucl Recept Signal. 4:e203, 2006.
Lambertini M, Santoro L, Del Mastro L, et al. Reproductive behaviors and risk of developing breast cancer according to tumor subtype: A systematic review of meta-analysis of epidemiological studies. Cancer Treat Rev. 2016; 49:65-76.
Dietel M, Lewis M, Shapiro S. Hormone replacement therapy: pathobiological aspects of hormone-sensitive cancers in women relevant to epidemiological studies on HRT: a mini-review. Human Reprod. 20(8):2052-2060, 2005.
Colditz, et al. Postmenopausal estrogen and progestin use and the risk of cardiovascular disease. N Eng J Med. 335:453-461, 1996.
Beral V. Million Women Study Collaborators. Breast cancer and hormone-replacement therapy in the Million Women Study. Lancet. 2003; 362:419–427.
Baber RJ, Panay N, Fenton A, for the IMS Writing Group. 2016 IMS Recommendations on women’s midlife health and menopause hormone therapy. Climacteric 2016;19:109–50
Grodstein F, et al. Postmenopausal estrogen and progestin use and the risk of cardiovascular disease. N Engl J Med. 1996.
Karim R, Dell RM, Greene DF, et al. Hip fracture in postmenopausal women after cessation of hormone therapy: results from a prospective study in a large health management organization. Menopause 2011;18:1172–7
Mikkola TS, Tuomikoski P, Lyytinen H, et al. Increased cardiovascular mortality risk in women discontinuing postmenopausal hormone therapy. J Clin Endocrinol Metab 2015;100:4588–94
Ravdin PM, Cronin KA, Howlader N, et al. The decrease in breast-cancer incidence in 2003 in the United States. N Engl J Med 2007;356:1670 – 74)
Jemal A, Ward E, Thun M. Recent trends in breast cancer incidence rates by age and tumor characteristics among U.S. women. Breast Cancer Res 2007;9:R28
Glass AG, Lacey JV, Carreon JD, Hoover RN. Breast cancer incidence, 1980 – 2006: combined roles of menopausal hormone Hormone therapy and breast cancer risk therapy, screening mammography, and estrogen receptor status. J Natl Cancer Inst
2007;99:1152 – 61
Caan B, Habel L, Quesenberry C, Kushi L, Herrinton L. Re: Declines in invasive breast cancer and use of postmenopausal hormone therapy in a screening mammography population. J Natl Cancer Inst 2008;100:597 – 98
Zahl P-H, Maehlen J. A decline in breast-cancer incidence. N Engl J Med 2007;357:510 – 11
Kumle M, Weiderpass E, Braaten T, et al. Use of oral contraceptives and breast cancer risk: the Norwegian–Swedish women’s lifestyle and health cohort study. Cancer Epidemiol Biomark Prev. 2002;11:1375–1381.
Marchbanks PA, McDonald JA, Wilson HG, et al. Oral contraceptives and the risk of breast cancer. N Engl J Med. 2002;346:2025–2032.
Strom BL, Berlin JA, Weber AL, et al. Absence of an effect of injectable and implantable progestin-only contraceptives on subsequent risk of breast cancer. Contraception. 2004;69: 353–360.
Backman T, Rauramo I, Jaakkola K, et al. Use of the levonorgestrel-releasing intrauterine system and breast cancer. Obstet Gynecol. 2005; 106:813–817.
T. Soini, R. Hurskainen, S. Grenman, J. Mäenpää, J. Paavonen, et al.Cancer risk in women using the levonorgestrel-releasing intrauterine system in Finland. Obstet Gynecol, 124 (2 Pt 1)(2014), pp.292-299.
Dinger, et al. Levonorgestrel-releasing and copper intrauterine devices and the risk of breast cancer. Contraception. 83 (3):211-217, 2011.
Mørch LS, Skovlund CW, Hannaford PC, Iversen L, Fielding S, Lidegaard Ø. Contemporary hormonal contraception and the risk of breast cancer. N Engl J Med 2017;377:2228-39.
References

2. Biglia, Peano et al. Low-dose vaginal estrogens or vaginal moisturizer in breast cancer survivors with urogenital atrophy: a preliminary study. Gyn Endocrinology 26 (6): 404-412, 2010.
Dew JE, Wren BG, Eden HA. A cohort study of topical vaginal estrogen therapy in women previously treated for breast cancer. Climacteric. 6: 45-52, 2003.
Lyons T. Postpartum mammary gland involution drives progression of ductal carcinoma in situ through collagen and COX-2. Nat Med. 2011;17:1109.
HERS study Hulley S, Grady D, Bush T, et al. Randomized Trial of Estrogen Plus Progestin for Secondary Prevention of Coronary Heart Disease in Postmenopausal Women. JAMA. 1998;280(7):605–613. doi:10.1001/jama.280.7.605
Li C, Malone K, Daling J, et al. Timing of menarche and first full-term birth in relation to breast cancer risk. Am J Epidemiol. 2008;167: 230–239.
Clark JH. A critique of Women's Health Initiative Studies (2002-2006). Nucl Recept Signal. 2006;4:e023. Published 2006 Oct 30. doi:10.1621/nrs.04023
Fournier, et al. Unewqual risks for breast cancer associated with different hormone replacement therapies: results from the E3N cohort study. Breast Cancer Ris Treat. 107 (1):103-111, 2008.
Crandall C, et al. Comparison of clinical outcomes among users of oral and transdermal estrogen therapy in the Women’s Health Oinitiative Observationnal Study. Menopause. 24 (10): 1134-1153, 2017.
Lee JS, Ettinger B, Stanczyk F, et al. Comparison of methods to measure low serum estradiol levels in postmenopausal women. J Clin Endocrinol Metab. 91(10):3791-7, 2006.
Kushnir M, Rockwood A, Bergquist J, et al. High-sensitivity tandem mass spectrometry assay for serum estrone and estradiol. Am J Clin Pathol. 129(4):530-9, 2008.
Crandall C, et al. Breast cancer, endometrial cancer, and cardiovascular events in participants who used vaginal estrogen in the Women’s Health Initiative Observational Study. Menopause. 25 (1):11-20, 2018.
Writing group for the Women’s Health Initiative Investigators. Risks and benefits of estrogen plus progestin in healthy postmenopausal women. JAMA. 288 (3):321-333.
Baber RJ, Panay N, Fenton A, for the IMS Writing Group. 2016 IMS Recommendations on women’s midlife health and menopause hormone therapy. Climacteric 2016;19:109–50.
Dietel M, et al. Hormone replacement therapy: pathobiological aspects of hormone-sensitive cancers in women relevant to epidemiological studies on HRT: a mini-review. Human Reprod. 20 (8):2052-60, 2005.
Fraumeni J, et al. Cancer mortality among nuns: role of marital status in neoplastic diseases of women. J Natl Cancer Inst. 42 (3):455-468, 1969.
ACOG CO No 659: The use of vaginal estrogen in women with a history of estrogen-dependent breast cancer. Obstet Gynecol. 127(3):618-619, 2016.
Fisher, et al. A randomized clinical trial evaluating tamoxifen in the treatment of patients with node-negative breast cancer who have estrogen-receptor-positive tumors. N Engl J Med. 320:479-484, 1989.
Fisher, et al. Tamoxifen for prevention of breast cancer… JNCI. 90 (18): 1371-1388, 1998.
Hulley, et al. Randomized trial of estrogen plus progestin for secondary prevention of coronary heart disease in postmenopausal women. JAMA. 280 (7):605-613, 1998.
References