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What is Endocrine Therapy?

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About 70% of breast cancers are hormone receptor positive, which means that the breast cancer has receptors on the surface of the cells for hormones called estrogen or progesterone.

If you have this type of cancer, it is usually recommended that you start on a type of medicine called endocrine therapy after completing your primary breast cancer treatment (surgery, chemo, and/or radiation).

It is generally recommended that women take this medication for 5-10 years. Endocrine therapy can reduce the risk of breast cancer coming back by 50%.

Types of Endocrine Therapy

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Estrogen Blockers: These prevent estrogen from binding to cancer cell receptors. These drugs include: Tamoxifen, toremifene (Fareston), and fulvestrant (Faslodex).

Estrogen Reducers: These drugs reduce the amount of estrogen your body makes. They are also called Aromatase Inhibitors and include: letrozole (Femara), anastrozole (Arimidex), and exemestane (Aromasin).

Other names for Endocrine Therapy: hormonal therapy, anti-estrogen therapy, aromatase inhibitors (“AIs”).

You may also receive other treatments to stop your ovarian cycles along with your endocrine therapy medication. These treatments are often called “ovarian suppression” or “ovarian ablation”.

Your doctor will recommend a particular drug for you based on several factors, including your age, whether you still have a monthly menstrual cycle, other health conditions, or other medications you take.

Hormone Therapy vs. Hormone Replacement Therapy

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It is easy to confuse endocrine therapy with other medications, and the names of medications add to the confusion. Although some doctors and patients call these breast cancer medications “hormone therapy”, it’s important to remember that breast cancer medications like tamoxifen and aromatase inhibitors are actually estrogen-blocking or estrogen-reducing medicines. They should not be confused with Hormone Replacement Therapy (HRT) that may be used during menopause, or oral contraceptives (“birth control pills”), which are pill forms of estrogen and/or progesterone hormones. Endocrine therapy for breast cancer is also different than medicines used to treat other hormonal imbalances such as hypothyroidism.

Bottom line: endocrine therapies are NOT hormones. They are hormone blockers or reducers.

Endocrine Therapy Research

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Patterns of Endocrine Therapy Use

  • Davies C, Pan H, Godwin J, et al. Long-term effects of continuing adjuvant tamoxifen to 10 years versus stopping at 5 years after diagnosis of oestrogen receptor-positive breast cancer: ATLAS, a randomised trial. Lancet. 2013;381(9869):805-816. doi:10.1016/S0140-6736(12)61963-1. Read article
  • Farias AJ, Du XL. Association Between Out-Of-Pocket Costs, Race/Ethnicity, and Adjuvant Endocrine Therapy Adherence Among Medicare Patients With Breast Cancer. J Clin Oncol. 35:86-95. doi:10.1200/JCO.2016.68.2807. Read article
  • Wheeler SB, Spencer J, Pinheiro LC, Murphy CC, Earp JA, Carey L, Olshan A, Tse CK, Bell ME, Weinberger M, Reeder-Hayes KE. Endocrine Therapy Nonadherence and Discontinuation in Black and White Women. J Natl Cancer Inst. 2019 May 1;111(5):498-508. doi: 10.1093/jnci/djy136. PMID: 30239824. Read article
  • Pinheiro LC, Wheeler SB, Reeder-Hayes KE, Samuel CA, Olshan AF, Reeve BB. Investigating Associations Between Health-Related Quality of Life and Endocrine Therapy Underuse in Women With Early-Stage Breast Cancer. J Oncol Pract. 2017 May;13(5):e463-e473. doi: 10.1200/JOP.2016.018630. Epub 2017 Mar 14. PMID: 28291383. Read article
  • Wheeler SB, Roberts MC, Bloom D, Reeder-Hayes KE, Espada M, Peppercorn J, Golin CE, Earp JA. Oncology providers' perspectives on endocrine therapy prescribing and management. Patient Prefer Adherence. 2016 Sep 30;10:2007-2019. PMID: 27757021. Read article
  • Wheeler SB, Kohler RE, Reeder-Hayes KE, Goyal RK, Lich KH, Moore A, Smith TW, Melvin CL, Muss HB. Endocrine therapy initiation among Medicaid-insured breast cancer survivors with hormone receptor-positive tumors. J Cancer Surviv. 2014 Dec; 8 (4): 603-10. doi: 10.1007/s11764-014-0365-3. Epub 2014 May 28. PMID: 24866922. Read article
  • Reeder-Hayes KE, Meyer AM, Dusetzina S, Liu H, Wheeler SB. Racial disparities in initiation of adjuvant endocrine therapy of early breast cancer. Breast Cancer Res Treat. 2014 Jun; 145(3): 743-51 doi: 10.1007/s10549-014-2957-z. Epub 2014 May 1. PMID: 24789443. Read article
  • Roberts MC, Wheeler SB, Reeder-Hayes K. Racial/Ethnic and Socioeconomic Disparities in Endocrine Therapy Adherence in Breast Cancer: A Systematic Review. Am J Public Health. Am J Public Health. 2015 Jul;105 Suppl 3:e4-e15. doi: 10.2105/AJPH.2014.302490. Epub 2015 Apr 23. PMID: 25905855. Read article
  • Kohler RE, Wheeler SB, Reeder-Hayes KE, Goyal RK, Lich KH, Smith T, Melvin C, Moore A, Muss HB. Endocrine therapy use among Medicaid-insured breast cancer survivors with hormone receptor-positive tumors. J Clin Oncol 2012 May 20;30(15):6017. Read article
  • Farias AJ, Du XL. Racial Differences in Adjuvant Endocrine Therapy Use and Discontinuation in Association with Mortality among Medicare Breast Cancer Patients by Receptor Status. Cancer Epidemiol Biomarkers Prev. 2017;26(8):1266-1275. doi:10.1158/1055-9965.EPI-17-0280. Read article
  • Hershman DL, Kushi LH, Shao T, et al. Early Discontinuation and Nonadherence to Adjuvant Hormonal Therapy in a Cohort of 8,769 Early-Stage Breast Cancer Patients. J Clin Oncol. 2010;28(27):4120-4128. doi:10.1200/jco.2009.25.9655. Read article
  • Hershman DL, Shao T, Kushi LH, et al. Early discontinuation and non-adherence to adjuvant hormonal therapy are associated with increased mortality in women with breast cancer. Breast Cancer Res Treat. 2011;126(2):529-537. doi:10.1007/s10549-010-1132 Read article

Barriers to endocrine therapy use

  • Wheeler SB, Spencer JC, Pinheiro LC, Carey LA, Olshan AF, Reeder-Hayes KE. Financial Impact of Breast Cancer in Black Versus White Women. J Clin Oncol. 2018 Jun 10;36(17):1695-1701. doi: 10.1200/JCO.2017.77.6310. Epub 2018 Apr 18. PMID: 29668368. Read article
  • Bright EE, Petrie KJ, Partridge AH, Stanton AL. Barriers to and facilitative processes of endocrine therapy adherence among women with breast cancer. Breast Cancer Res Treat. 2016;158(2):243-251. doi:10.1007/s10549-016-3871-3. Read article
  • Walker HE, Rosenberg SM, Stanton AL, Petrie KJ, Partridge AH. Perceptions, Attributions, and Emotions Toward Endocrine Therapy in Young Women with Breast Cancer. J Adolesc Young Adult Oncol. 2016;5(1):16-23. doi:10.1089/jayao.2015.0051. Read article
  • Spencer JC, Samuel CA, Rosenstein DL, Reeder-Hayes KE, Manning ML, Sellers JB, Wheeler SB. Oncology navigators' perceptions of cancer-related financial burden and financial assistance resources. Support Care Cancer. 2018 Apr;26(4):1315-1321. doi: 10.1007/s00520-017-3958-3. Epub 2017 Nov 9. PMID: 29124417. Read article
  • Spencer JC+, Reeve BB, Troester MA, Wheeler SB. Factors Associated with Endocrine Therapy Non-Adherence in Breast Cancer Survivors. Psychooncology. 2020 Apr;29(4):647-654. doi: 10.1002/pon.5289. Epub 2020 Feb 11. PMID: 32048400. Read article
  • Wheeler SB, Spencer J++, Pinheiro LC+, Murphy CC+, Earp JA, Carey L, Olshan A, Tse CK, Bell ME, Weinberger M, Reeder-Hayes KE. Endocrine Therapy Nonadherence and Discontinuation in Black and White Women. J Natl Cancer Inst. 2019 May 1;111(5):498-508. doi: 10.1093/jnci/djy136. PMID: 30239824. Read article

Strategies to help women taking endocrine therapy

  • Krok-Schoen J, Naughton MJ, Young GS, Moon J, Paskett ED, Post DM. Increasing Adherence to Adjuvant Hormone Therapy among Breast Cancer Patients: A Smart Phone App-Based Pilot Study. Cancer Control. 2019; 26(1):1-10. doi: 10.1177/1073274819883287. PMID:31736324 Read article
  • Ekinci E, Nathoo S, Korattyil T, Vadhariya A, Zaghloul HA. Interventions to improve endocrine therapy adherence in breast cancer survivors: what is the evidence? J Cancer Surviv. 2018. doi:10.1007/s11764-017-0674-4. Read article
  • Palacio A, Garay D, Langer B, Taylor J, Wood BA, Tamariz L. Motivational Interviewing Improves Medication Adherence: a Systematic Review and Meta-analysis. J Gen Intern Med. 2016;31(8):929-940. doi:10.1007/s11606-016-3685-3. Read article
  • Mougalian SS, Epstein LN, Jhaveri AP, et al. Bidirectional Text Messaging to Monitor Endocrine Therapy Adherence and Patient-Reported Outcomes in Breast Cancer. JCO Clin Cancer Informatics. 2017;(1):1-10. doi:10.1200/CCI.17.00015. Read article

"I want to know I’m doing everything I can to stay healthy”
- Study participant

This work is supported through a National Cancer Institute (NCI) award (RO1CA237357-01), and through the Alliance for Clinical Trials in Oncology’s NCORP.