Is there a correlation between HER2 gene amplification level and response to neoadjuvant treatment with trastuzumab and chemotherapy in HER2-positive breast cancer?

There are contradictory data regarding the correlation between HER2 amplification level determined by in situ hybridization and evolution after treatment with anti-HER2 therapies. The aim of this study was to correlate quantitative results of FISH (ratio HER2/CEP17 and number of HER2 signals/nucleus) with pathological response achieved after neoadjuvant treatment with trastuzumab and chemotherapy. For this purpose, we analysed 100 consecutive HER2-positive cases of breast carcinoma treated with neoadjuvant therapy. HER2 amplification determined by FISH was found in 92 of the 100 cases studied. pCR was obtained in 58% of the patients whose tumours presented amplification. In contrast, no pCR was obtained in the 8 patients with non-amplified tumours. A significant direct correlation between HER2 high amplification (HER2/CEP17 ratio > 5 or HER2 signals/nucleus > 10) and pCR was found. In conclusion, HER2 amplification levels are clinically relevant because they provide oncologists with valuable information on the possibilities of achieving pCR after neoadjuvant treatment.