Retrospective observational study of HER2 immunohistochemistry in borderline breast cancer patients undergoing neoadjuvant therapy, with an emphasis on Group 2 (HER2/CEP17 ratio ≥2.0, HER2 copy number

Emad A. Rakha (Lead / Corresponding author), Islam M. Miligy, Cecily M. Quinn, Elena Provenzano, Abeer M. Shaaban, Caterina Marchiò, Michael S. Toss, Grace Gallagy, Ciara Murray, Janice Walshe, Ayaka Katayama, Karim Eldib, Nahla Badr, Bruce Tanchel, Rebecca Millican-Slater, Colin Purdie, Dave Purnell, Sarah E. Pinder, Ian O. Ellis, Andrew H. S. Lee

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Abstract

Background: The ASCO/CAP guidance on HER2 testing in breast cancer (BC) has recently changed. Group 2 tumours with immunohistochemistry score 2+ and HER2/CEP17 ratio ≥2.0 and HER2 copy number <4.0 signals/cell were re-classified as HER2 negative. This study aims to examine the response of Group 2 tumours to neoadjuvant chemotherapy (NACT).

Methods: 749 BC cases were identified from 11 institutions. The association between HER2 groups and pathological complete response (pCR) was assessed.

Results: 54% of immunohistochemistry HER2 positive (score 3+) BCs showed pCR, compared to 19% of immunohistochemistry 2+ FISH amplified cases. 27% of Group 2 treated with HER2 targeted therapy achieved pCR, compared to 19 and 11% in the combined Groups 1 + 3 and Groups 4 + 5, respectively. No difference in pCR rates was identified between Group 2 and Group 1 or combined Groups 1 + 3. However, Group 2 response rate was higher than Groups 4 + 5 (p = 0.017).

Conclusion: No difference in pCR was detected in tumours with a HER2/CEP17 ratio ≥2.0 and a HER2 score 2+ by IHC when stratified by HER2 gene copy number. Our data suggest that ASCO/CAP HER2 Group 2 carcinomas should be evaluated further with respect to eligibility for HER2 targeted therapy.

Original languageEnglish
Number of pages7
JournalBritish Journal of Cancer
Early online date24 Mar 2021
DOIs
Publication statusE-pub ahead of print - 24 Mar 2021

Keywords

  • Breast cancer

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