A Nationwide Study on HER2-low Breast Cancer in South Korea: Its Incidence of 2022 Real World Data and the Importance of Immunohistochemical Staining Protocols
1Department of Pathology, Yeungnam University College of Medicine, Daegu, Korea 2Department of Pathology and Translational Genomics, Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul, Korea 3Department of Pathology, Seoul National University Bundang Hospital, Seoul National University College of Medicine, Seongnam, Korea 4Department of Pathology, Asan Medical Center, University of Ulsan College of Medicine, Seoul, Korea 5Department of Pathology, Chonnam National University Medical School, Gwangju, Korea 6Department of Pathology, Pusan National University Yangsan Hospital, Pusan National University School of Medicine, Yangsan, Korea 7Department of Pathology, Chungbuk National University College of Medicine, Cheongju, Korea 8Department of Pathology, Saegyaero Hospital, Busan, Korea 9Department of Pathology, Chung-Ang University College of Medicine, Seoul, Korea 10Department of Pathology, Inje University Haeundae Paik Hospital, Inje University College of Medicine, Busan, Korea 11Department of Pathology, Konkuk University School of Medicine, Seoul, Korea 12Department of Pathology, Good Gang-an Hospital, Busan, Korea 13Department of Pathology, Jeju National University School of Medicine, Jeju, Korea 14Department of Pathology, Wonkwang University Hospital, Wonkwang University School of Medicine, Iksan, Korea 15Department of Pathology, Keimyung University School of Medicine, Daegu, Korea 16Department of Pathology, Korea University Guro Hospital, Korea University College of Medicine, Seoul, Korea 17Department of Pathology, Incheon St. Mary’s Hospital, College of Medicine, The Catholic University of Korea, Incheon, Korea 18Department of Pathology, Seoul Clinical Laboratories, Yongin, Korea 19Department of Pathology, Ulsan University Hospital, Ulsan University, College of Medicine, Ulsan, Korea 20Department of Pathology, Chungnam National University Sejong Hospital, Sejong, Korea 21Department of Pathology, Jeonbuk National University Medical School, Jeonju, Korea 22Department of Pathology, St. Vincent’s Hospital, College of Medicine, The Catholic University of Korea, Suwon, Korea 23Department of Pathology, Nowon Eulji University Hospital, Seoul, Korea 24Department of Pathology, Pusan National University Hospital, Busan, Korea 25Department of Pathology, CHA Gangnam Medical Center, CHA University School of Medicine, Seoul, Korea
Correspondence
Gyungyub Gong ,Tel: 82-2-2010-4554, Fax: 82-2-472-7898, Email: gygong@amc.seoul.kr Young Kyung Bae ,Tel: 82-53-640-6755 , Fax: 82-53-622-8432, Email: ykbae@ynu.ac.kr
Received: January 25, 2024; Accepted: March 4, 2024. Published online: March 6, 2024. *Min Chong Kim and Eun Yoon Cho contributed equally to this work.
ABSTRACT
Purpose
Notable effectiveness of trastuzumab deruxtecan (T-DXd) in patients with HER2-low advanced breast cancer (BC) has focused pathologists’ attention. We studied the incidence and clinicopathologic characteristics of HER2-low BC, and the effects of immunohistochemistry (IHC) associated factors on HER2 IHC results.
Materials and Methods
The Breast Pathology Study Group of the Korean Society of Pathologists conducted a nationwide study using real-world data on HER2 status generated between January 2022 and December 2022. Information on HER2 IHC protocols at each participating institution was also collected.
Results
Total 11,416 patients from twenty-five institutions included in this study. Of these patients, 40.7% (range: 6.0%–76.3%) were classified as HER2-zero, 41.7% (range: 10.5%–69.1%) as HER2-low, and 17.5% (range: 6.7%–34.0%) as HER2-positive. HER2-low tumors were associated with positive ER and PR statuses (p<0.001 and p<0.001, respectively). Antigen retrieval times (≥ 36 min vs. < 36 min) and antibody incubation times (≥ 12 min vs. < 12 min) affected on the frequency of HER2 IHC 1+ BC at institutions using the PATHWAY HER2 (4B5) IHC assay and BenchMark XT or Ultra staining instruments. Furthermore, discordant results between core needle biopsy (CNB) and subsequent resection specimen HER2 statuses were observed in 24.1% (787/3259) of the patients.
Conclusion
The overall incidence of HER2-low BC in South Korea concurs with those reported in previously published studies. Significant inter-institutional differences in HER2 IHC protocols were observed, and it may have impact on HER2-low status. Thus, we recommend standardizing HER2 IHC conditions to ensure precise patient selection for targeted therapy.
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