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)

Affiliations
  • 1Department of Surgery, Gangnam Severance Hospital, Seoul, Korea
  • 2Department of Surgery, Samsung Medical Center, Seoul, Korea
  • 3Department of Surgery, Asan Medical Center, Seoul, Korea
  • 4Department of Surgery, Ajou University School of Medicine, Suwon, Korea
  • 5Department of Surgery, Gachon University Gil Hospital, Incheon, Korea
  • 6Department of Surgery, Yeungnam University College of Medicine, Daegu, Korea
  • 7Department of Surgery, CHA University Ilsan Medical Center, Goyang, Korea
  • 8Department of Surgery, Seoul National University College of Medicine, Seoul, Korea
  • 9Division of Oncology/Hematology, Department of Internal Medicine, Korea University College of Medicine, Seoul, Korea
  • 10Department of Surgery, Kangbuk Samsung Hospital, Seoul, Korea
  • 11Department of Surgery, Soonchunhyang University Seoul Hospital, Seoul, Korea
  • 12Department of Surgery, Jeonbuk National University Medical School, Jeonju, Korea
  • 13Department of Surgery, Busan St. Mary's Hospital, Busan, Korea
  • 14Department of Surgery, Konkuk University Medical Center, Choongju, Korea
  • 15Department of Surgery, Kyung Hee University Hospital, Seoul, Korea
  • 16Department of Surgery, Ulsan University Hospital, Ulsan, Korea
  • 17Department of Surgery, Inje University Sanggye Paik Hospital, Seoul, Korea
  • 18Department of Surgery, Hanyang University Hospital, Seoul, Korea
  • 19Department of Surgery, Soonchunhyang University Cheonan Hospital, Cheonan, Korea
  • 20Department of Surgery, Dong-A University Hospital, Busan, Korea
  • 21Department of Surgery, Kangseo MizMedi Hospital, Seoul, Korea
  • 22Department of Surgery, Dankook University Hospital, Cheonan, Korea
  • 23Department of Surgery, Ewha Woman's University Mokdong Hospital, Seoul, Korea
  • 24Department of Surgery, Hallym University Sacred Heart Hospital, Anyang, Korea
  • 25Department of Surgery, Gangseo Mizmedi Hospital, Seoul, Korea
  • 26Department of Surgery, Chonnam National University Medical School, Gwangju, Korea
  • 27Department of Surgery, Inje University Busan Paik Hospital, Busan, Korea
  • 28Department of Surgery, Keimyung University School of Medicine, Daegu, Korea
  • 29Department of Surgery, Soonchunhyang University Bucheon Hospital, Bucheon, Korea
  • 30Department of Surgery, Pusan National University Hospital, Busan, Korea
  • 31Department of Pathology, Asan Medical Center, Seoul, Korea
  • 32Department of Pathology, Yeungnam University College of Medicine, Daegu, Korea
  • 33Department of Pathology, Seoul St. Mary's Hospital, The Catholic University of Korea, Seoul, Korea

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
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