[Efficacy of neoadjuvant therapy on HER2-positive breast cancer: a clinicopathological analysis]

Objective: To investigate the efficacy of neoadjuvant therapy (NAT) on HER2-positive breast cancer and to analyze their clinicopathological features. Methods: A total of 480 cases of HER2-positive breast cancer who received neoadjuvant therapy (NAT), diagnosed at the Department of Pathology of Fudan University Shanghai Cancer Center from 2015 to 2020, were retrospectively identified. Clinicopathological parameters such as age, tumor size, molecular subtype, type of targeted therapy, Ki-67 proliferation index, ER and HER2 immunohistochemical expression, and HER2 amplification status were analyzed to correlate with the efficacy of NAT. Results: Among 480 patients with HER2-positive breast cancer, 209 achieved pathology complete response (pCR) after NAT, with a pCR rate of 43.5%. Of all the cases,457 patients received chemotherapy plus trastuzumab and 23 patients received chemotherapy with trastuzumab and pertuzumab. A total of 198 cases (43.3%) achieved pCR in patients with chemotherapy plus trastuzumab, and 11 cases (47.8%) achieved pCR in patients with chemotherapy plus trastuzumab and pertuzumab. The pCR rate in the latter group was higher, but there was no statistical significance. The results showed that the pCR rate of IHC-HER2 3+patients (49%) was significantly higher than that of IHC-HER2 2+patients (26.1%, P<0.001). The higher the mean HER2 copy number in the FISH assay, the higher the pCR rate was achieved. The expression level of ER was inversely correlated with the efficacy of NAT, and the pCR rate in the ER-positive group (28.2%) was significantly lower than that in the ER-negative group (55.8%, P<0.001). The pCR rate (29.1%) of patients with luminal B type was lower than that of HER2 overexpression type (55.8%, P<0.001). In addition, higher Ki-67 proliferation index was associated with higher pCR rate (P<0.001). The pCR rate was the highest in the tumor ≤2 cm group (57.7%), while the pCR rate in the tumor >5 cm group was the lowest (31.1%). The difference between the groups was significant (P=0.005). Conclusions: HER2 copy numbers, HER2 immunohistochemical expression level, molecular subtype, ER expression level and Ki-67 proliferation index are significantly associated with pCR after NAT. In addition, fluorescence in situ hybridization results, HER2/CEP17 ratio and tumor size could also significantly affect the efficacy of NAT.