Clinical outcomes following letrozole treatment according to estrogen receptor expression in postmenopausal women: LETTER study (KBCSG-006)

Sung Gwe Ahn, Seok Jin Nam, Sei Hyun Ahn, Yongsik Jung, Heung Kyu Park, Soo Jung Lee, Sung Soo Kang, Wonshik Han, Kyong Hwa Park, Yong Lai Park, Jihyoun Lee, Hyun Jo Youn, Jun Hyun Kim, Youngbum Yoo, Jeong Yoon Song, Byung Kyun Ko, Geumhee Gwak, Min Sung Chung, Sung Yong Kim, Seo Heon ChoDoyil Kim, Myung Chul Chang, Byung In Moon, Lee Su Kim, Sei Joong Kim, Min Ho Park, Tae Hyun Kim, Jihyoung Cho, Cheol Wan Lim, Young Tae Bae, Gyungyub Gong, Young Kyung Bae, Ahwon Lee, Joon Jeong

Research output: Contribution to journalArticlepeer-review

1 Scopus citations


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.

Original languageEnglish
Pages (from-to)164-174
Number of pages11
JournalJournal of Breast Cancer
Issue number2
StatePublished - 2021

Bibliographical note

Publisher Copyright:
© 2021 Korean Breast Cancer Society.


  • Breast neoplasms
  • Estrogen
  • Letrozole
  • Postmenopause
  • Receptors


Dive into the research topics of 'Clinical outcomes following letrozole treatment according to estrogen receptor expression in postmenopausal women: LETTER study (KBCSG-006)'. Together they form a unique fingerprint.

Cite this