Immunohistochemical HER2 score correlates with response to neoadjuvant chemotherapy in HER2-positive primary breast cancer
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Updated: Nov 17, 2025
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Published on: May 9, 2025
Yihong Wang1, Kamaljeet Singh2, Don Dizon3
1Department of Pathology and Laboratory Medicine, Rhode Island Hospital and Lifespan Medical Center, Warren Alpert Medical School of Brown University, 593 Eddy St, APC 12, Providence, RI, 02903, USA. yihong_wang@brown.edu.
Purpose:
The accuracy of biomarker assessment in breast cancer (BC) is paramount for therapy decisions and informs prognosis. We investigated neoadjuvant chemotherapy (NAC) response in HER2-positive BC with respect to immunohistochemistry (IHC) and in situ hybridization (ISH) results. We aimed to determine the role of HER2 protein expression in predicting NAC response and long-term outcome in two HER2-positive groups: IHC 3 + versus IHC 2 + ISH amplified groups.
Methods:
This retrospective study included 192 consecutive HER2 + primary BCs diagnosed from 2007 to 2019 treated with NAC and HER2-targeted agent (NACH). There were 158 HER2 3 + and 34 HER2 2 + ISH + cases. Clinicopathological parameters and long-term outcomes were analyzed.
Results:
The Pathological Complete Response (pCR) rate was 85.7% (72/84) in ER-/HER2 + BCs and was lower in ER + /HER2 + BCs (42.6%, 46/108). The pCR was 55.1% (86/156) in the HER2 3 + group and was only 17.6% in HER2 2 + ISH + group (p < 0.001). Patients who achieved pCR in HER2 2 + ISH + group did not show a significantly higher HER2/CEP17 ratio or HER2 copy number. The overall survival (OS) and progression-free survival (PFS) were significantly higher in pCR compared to non-pCR cases (p = 0.011 and p = 0.015, respectively).
Conclusions:
There is significant heterogeneity in response to the NACH regimens in HER2 + cases. Our findings indicate that HER2 IHC score and ER expression determine NACH response in HER2 + BC. We recommend considering HER2 protein expression and ISH value to better select patients and assess the response for HER2-targeted therapy.
