This summary table contains detailed information about research studies. Summary tables are a useful way to look at the science behind many breast cancer guidelines and recommendations. However, to get the most out of the tables, it’s important to understand some key concepts. Learn how to read a research table.

Introduction: Hormone therapy is a standard treatment for hormone receptor-positive breast cancers (estrogen and/or progesterone receptor-positive cancers). It’s not used to treat hormone receptor-negative breast cancers.

Hormone therapy drugs include tamoxifen and aromatase inhibitors.

Hormone therapy may be given before breast surgery (called neoadjuvant hormone therapy) to try to shrink the tumor enough so a lumpectomy becomes an option to a mastectomy.  

Findings to date are mainly from studies of women 70 years and older. For women in this age group, some standard treatments (surgery and/or chemotherapy) may not be recommended for health reasons.

For postmenopausal women, neoadjuvant hormone therapy with an aromatase inhibitor appears to offer more benefit and fewer serious side effects than with tamoxifen [1-5]. 

Learn more about neoadjuvant hormone therapy.

Learn about the strengths and weaknesses of different types of studies.

Study selection criteria: Phase III randomized clinical trials with 100 or more participants.  

Study	Study Population (number of participants)	Type of Aromatase Inhibitor	Duration of Neoadjuvant Treatment	Clinical Response and Rate of Lumpectomy with Neoadjuvant Aromatase Inhibitor vs. Neoadjuvant Tamoxifen
Randomized Clinical Trials
Ellis et al. and Eiermann et al. [1-2]	324 postmenopausal women	Letrozole	4 months	Clinical response: letrozole = 55% vs. tamoxifen = 36% Lumpectomy: letrozole = 45% vs. tamoxifen = 35%
PROACT Trial [3]	314 postmenopausal women	Anastrozole	3 months	Clinical response: anastrozole = 50% vs. tamoxifen = 40% Lumpectomy: anastrozole = 43% vs. tamoxifen = 31%
Ellis et al. [1]	250 postmenopausal women	Letrozole	4 months	Clinical response: letrozole = 60% vs. tamoxifen = 41% Lumpectomy: letrozole = 48% vs. tamoxifen = 36%
IMPACT Trial [4]	221 postmenopausal women	Anastrozole	3 months	Clinical response: anastrozole = 37% vs. tamoxifen = 36% Lumpectomy: anastrozole = 44% vs. tamoxifen = 31%
Study	Study Population (number of participants)	Type of Aromatase Inhibitor	Duration of Neoadjuvant Treatment	Clinical Response and Rate of Lumpectomy with Neoadjuvant Aromatase Inhibitor
Ellis et al. [6]	377	Anastrozole, exemestane or letrozole	4 months	Clinical response: anastrozole = 69% exemestane = 63% letrozole = 75% Lumpectomy: anastrozole = 77% exemestane = 68% letrozole = 61%

References

1. Ellis MJ, Coop A, Singh B, et al. Letrozole is more effective neoadjuvant endocrine therapy than tamoxifen for ErbB-1- and/or ErbB-2-positive, estrogen receptor-positive primary breast cancer: evidence from a phase III randomized trial. J Clin Oncol. 19(18):3808-16, 2001.
2. Eiermann W, Paepke S, Appfelstaedt J, et al. for the Letrozole Neo-Adjuvant Breast Cancer Study Group. Preoperative treatment of postmenopausal breast cancer patients with letrozole: A randomized double-blind multicenter study. Ann Oncol. 12(11):1527-32, 2001.
3. Cataliotti L, Buzdar AU, Noguchi S, et al. Comparison of anastrozole versus tamoxifen as preoperative therapy in postmenopausal women with hormone receptor-positive breast cancer: the Pre-Operative “Arimidex” Compared to Tamoxifen (PROACT) trial. Cancer. 106(10):2095-103, 2006.
4. Smith IE, Dowsett M, Ebbs SR, et al. Neoadjuvant treatment of postmenopausal breast cancer with anastrozole, tamoxifen, or both in combination: the Immediate Preoperative Anastrozole, Tamoxifen, or Combined with Tamoxifen (IMPACT) multicenter double-blind randomized trial. J Clin Oncol. 23(22):5108-16, 2005.
5. Spring LM, Gupta A, Reynolds KL, et al. Neoadjuvant endocrine therapy for estrogen receptor–positive breast cancer: a systematic review and meta-analysis. JAMA Oncol. 2(11):1477-1486, 2016.
6. Ellis MJ, Suman VJ, Hoog J, et al. Randomized phase II neoadjuvant comparison between letrozole, anastrozole, and exemestane for postmenopausal women with estrogen receptor-rich stage 2 to 3 breast cancer: clinical and biomarker outcomes and predictive value of the baseline PAM50-based intrinsic subtype–ACOSOG Z1031. J Clin Oncol. 29(17):2342-9, 2011.

Updated 12/30/20