HER2 protein expression level is positively associated with the efficacy of neoadjuvant systemic therapy in HER2-positive breast cancer

The purpose of this study was to determine whether the HER2 protein expression level assessed by immunochemistry (IHC) was related to the treatment response in HER2-positive breast cancer patients who received neoadjuvant chemotherapy.167 HER2-positive breast cancer patients who had received neoadjuvant chemotherapy containing trastuzumab were included in this study. There were 27 HER2 2 + and 140 HER2 3 + cases. Using propensity score matching (PSM), the two groups were matched 1:3 by T stage, N stage, hormone receptor (HR) status, Ki67, and targeted therapy regimen. We performed univariate and multivariate analyses of the association between HER2 expression level and pathological complete response (pCR) rate.The overall pCR rate was 43.7% (73/167). The pCR rate in the HER2 3 + group was significantly higher than in the HER2 2 + group (47.9% versus 22.2%, p = 0.014). After propensity score matching, 26 patients in the HER2 2 + group and 59 patients in the HER2 3 + group were matched. The pCR rate in the HER2 3 + group was still higher than in the HER2 2 + group (50.8% versus 19.2%, p = 0.006). Multivariate analysis showed that HER2 protein expression was an independent predictive factor for pCR (OR=5.353, 95% CI 1.649-17.379, p = 0.005). Additionally, the Ki67 index was also a significant factor for pCR (OR=3.702, 95% CI 1.327-10.326, p = 0.012).For HER2-positive breast cancer patients, the HER2 protein expression level detected by IHC may be a good predictive factor for the efficacy of neoadjuvant chemotherapy.