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.
In some cases, hormone therapy may be given before breast surgery (called neoadjuvant hormone therapy) to try to reduce the size of 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 aromatase inhibitors appears to offer more benefit and fewer serious side effects than 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 Population(number of participants)
Type ofAromatase Inhibitor
Duration ofNeoadjuvant Treatment
Clinical Response andRate of Lumpectomy with Neoadjuvant Aromatase Inhibitor vs. Neoadjuvant Tamoxifen
Randomized Clinical Trials
Ellis et al. andEiermann et al. [1-2]
Clinical response:letrozole = 55% vs. tamoxifen = 36%
Lumpectomy:letrozole = 45% vs. tamoxifen = 35%
PROACT Trial 
Clinical response: anastrozole = 50% vs. tamoxifen = 40% Lumpectomy:anastrozole = 43% vs. tamoxifen = 31%
Ellis et al. 
Clinical response:letrozole = 60% vs. tamoxifen = 41%
Lumpectomy:letrozole = 48% vs. tamoxifen = 36%
IMPACT Trial 
Clinical response: anastrozole = 37% vs. tamoxifen = 36% Lumpectomy:anastrozole = 44% vs. tamoxifen = 31%
Clinical Response and Rate of Lumpectomy with Neoadjuvant Aromatase Inhibitor
Ellis et al. 
Anastrozole, exemestane or letrozole
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