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 &4.0 signals/cell) cases

摘要

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.