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. 2021 Apr;24(2):164-174.
doi: 10.4048/jbc.2021.24.e17. Epub 2021 Mar 25.

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

Sung Gwe Ahn  1 , Seok Jin Nam  2 , Sei Hyun Ahn  3 , Yongsik Jung  4 , Heung Kyu Park  5 , Soo Jung Lee  6 , Sung Soo Kang  7 , Wonshik Han  8 , Kyong Hwa Park  9 , Yong Lai Park  10 , Jihyoun Lee  11 , Hyun Jo Youn  12 , Jun Hyun Kim  13 , Youngbum Yoo  14 , Jeong Yoon Song  15 , Byung Kyun Ko  16 , Geumhee Gwak  17 , Min Sung Chung  18 , Sung Yong Kim  19 , Seo Heon Cho  20 , Doyil Kim  21 , Myung Chul Chang  22 , Byung In Moon  23 , Lee Su Kim  24 , Sei Joong Kim  25 , Min Ho Park  26 , Tae Hyun Kim  27 , Jihyoung Cho  28 , Cheol Wan Lim  29 , Young Tae Bae  30 , Gyungyub Gong  31 , Young Kyung Bae  32 , Ahwon Lee  33 , Joon Jeong  34
Affiliations

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

Sung Gwe Ahn et al. J Breast Cancer. 2021 Apr.

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.

Trial registration: ClinicalTrials.gov Identifier: NCT01069211.

Keywords: Breast neoplasms; Letrozole; Postmenopause; Receptors, estrogen.

PubMed Disclaimer

Conflict of interest statement

This study was funded by Novartis Korea. The funders provided the study drug (letrozole) and collaborated with the authors on the study design and data collection methods.

Figures

Figure 1
Figure 1. Clinical outcomes according to ER expression level (high, AS 7–8; low-to-intermediate, AS 3–6). Survival curves were generated using the Kaplan-Meier method. All p values were calculated using the log-rank test. (A) DFS (p = 0.6), (B) RFS (p = 0.7), (C) DMFS (p = 0.5), and (D) OS (p = 0.3).
ER = estrogen receptor; AS = Allred score; DFS = disease-free survival; RFS = recurrence-free survival; DMFS = distant metastasis-free survival; OS = overall survival.
Figure 2
Figure 2. Clinical outcome according to tumor, nodes, and metastases stage. Survival curves were generated using the Kaplan-Meier method. All p-values were calculated using the log-rank test. (A) DFS (p = 0.04), (B) RFS (p = 0.001), (C) DMFS (p = 0.001), and (D) OS (p < 0.001).
DFS = disease-free survival; RFS = recurrence-free survival; DMFS = distant metastasis-free survival; OS = overall survival.
Figure 3
Figure 3. AEs leading to drug discontinuation.
AE = adverse event.
See this image and copyright information in PMC

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