J Breast Cancer.  2021 Apr;24(2):164-174. 10.4048/jbc.2021.24.e17.

Clinical Outcomes Following Letrozole Treatment according to Estrogen Receptor Expression in Postmenopausal Women: LETTER Study (KBCSG-006)

• Ahn SG
• Nam SJ
• Ahn SH
• Jung Y
• Park HK
• Lee SJ
• Kang SS
• Han W
• Park KH
• Park YL
• Lee J
• Youn HJ
• Kim JH
• Yoo Y
• Song JY
• Ko BK
• Gwak G
• Chung MS
• Kim SY
• Cho SH
• Kim D
• Chang MC
• Moon BI
• Kim LS
• Kim SJ
• Park MH
• Kim TH
• Cho J
• Lim CW
• Bae YT
• Gong G
• Bae YK
• Lee A
• Jeong J

• KMID: 2515174
• DOI: http://doi.org/10.4048/jbc.2021.24.e17

Abstract

Purpose
In this trial, we investigated the efficacy and safety of adjuvant letrozole for hormone receptor (HR)-positive breast cancer. Here, we report the clinical outcome in postmenopausal women with HR-positive breast cancer treated with adjuvant letrozole according to estrogen receptor (ER) expression levels.
Methods
In this multi-institutional, open-label, observational study, postmenopausal patients with HR-positive breast cancer received adjuvant letrozole (2.5 mg/daily) for 5 years unless they experienced disease progression or unacceptable toxicity or withdrew their consent. The patients were stratified into the following 3 groups according to ER expression levels using a modified Allred score (AS): low, intermediate, and high (AS 3–4, 5–6, and 7–8, respectively). ER expression was centrally reviewed. The primary objective was the 5-year disease-free survival (DFS) rate.
Results
Between April 25, 2010, and February 5, 2014, 440 patients were enrolled. With a median follow-up of 62.0 months, the 5-year DFS rate in all patients was 94.2% (95% confidence interval [CI], 91.8–96.6). The 5-year DFS and recurrence-free survival (RFS) rates did not differ according to ER expression; the 5-year DFS rates were 94.3% and 94.1%in the low-to-intermediate and high expression groups, respectively (p = 0.6), and the corresponding 5-year RFS rates were 95.7% and 95.4%, respectively (p = 0.7). Furthermore, 25 patients discontinued letrozole because of drug toxicity.
Conclusion
Treatment with adjuvant letrozole showed very favorable treatment outcomes and good tolerability among Korean postmenopausal women with ER-positive breast cancer, independent of ER expression.

Keyword

Breast neoplasms; Letrozole; Postmenopause; Receptors; estrogen