Cancer Res Treat.  2024 Oct;56(4):1096-1104. 10.4143/crt.2024.092.

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

• Kim MC
• Cho EY
• Park SY
• Lee HJ
• Lee JS
• Kim JY
• Lee Hc
• Yoo JY
• Kim HS
• Kim B
• Kim WS
• Shin N
• Maeng YH
• Kim HS
• Kwon SY
• Kim C
• Jun SY
• Kwon GY
• Choi HJ
• Lee SM
• Choi JE
• An AR
• Choi HJ
• Kim E
• Kim A
• Kim JY
• Shim JY
• Gong G
• Bae YK

• KMID: 2560244
• DOI: http://doi.org/10.4143/crt.2024.092

Abstract

Purpose
Notable effectiveness of trastuzumab deruxtecan in patients with human epidermal growth factor receptor 2 (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 25 institutions included in this study. Of these patients, 40.7% (range, 6.0% to 76.3%) were classified as HER2-zero, 41.7% (range, 10.5% to 69.1%) as HER2-low, and 17.5% (range, 6.7% to 34.0%) as HER2-positive. HER2-low tumors were associated with positive estrogen receptor and progesterone receptor statuses (p < 0.001 and p < 0.001, respectively). Antigen retrieval times (≥ 36 minutes vs. < 36 minutes) and antibody incubation times (≥ 12 minutes vs. < 12 minutes) 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 and subsequent resection specimen HER2 statuses were observed in 24.1% (787/3,259) 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.

Keyword

Breast neoplasms; HER2-low; HER2-testing; Immunohistochemistry

Figure

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  Fig. 1. Proportions of human growth factor receptor 2 (HER2) statuses at the participating institutions.

Reference

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