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

• Published in: Journal of breast cancer Vol. 24; no. 2; pp. 164 - 174
• Main Authors: Ahn, Sung Gwe, Nam, Seok Jin, Ahn, Sei Hyun, Jung, Yongsik, Park, Heung Kyu, Lee, Soo Jung, Kang, Sung Soo, Han, Wonshik, Park, Kyong Hwa, Park, Yong Lai, Lee, Jihyoun, Youn, Hyun Jo, Kim, Jun Hyun, Yoo, Youngbum, Song, Jeong-Yoon, Ko, Byung Kyun, Gwak, Geumhee, Chung, Min Sung, Kim, Sung Yong, Cho, Seo Heon, Kim, Doyil, Chang, Myung-Chul, Moon, Byung In, Kim, Lee Su, Kim, Sei Joong, Park, Min Ho, Kim, Tae Hyun, Cho, Jihyoung, Lim, Cheol Wan, Bae, Young Tae, Gong, Gyungyub, Bae, Young Kyung, Lee, Ahwon, Jeong, Joon
• Format: Journal Article
• Language: English
• Published: Korea (South) Korean Breast Cancer Society 01.04.2021; 한국유방암학회
• Subjects: Original; 일반외과학; Postmenopause; Receptors, estrogen; Breast neoplasms; Letrozole
• ISSN: 1738-6756; 2092-9900
• DOI: 10.4048/jbc.2021.24.e17

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. 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. 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 ( = 0.6), and the corresponding 5-year RFS rates were 95.7% and 95.4%, respectively ( = 0.7). Furthermore, 25 patients discontinued letrozole because of drug toxicity. 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. ClinicalTrials.gov Identifier: NCT01069211.