Impact of HER2 immunohistochemistry score on pathological complete response and survival in HER2-positive breast cancer treated with neoadjuvant therapy: differential outcomes by hormone receptor status

Objective To investigate the impact of differences in HER2 protein expression level based on immunohistochemistry (IHC) score (HER2 3+ vs . HER2 2+/FISH+) on the pathological complete response (pCR) rate and patient prognosis in HER2-positive breast cancer treated with neoadjuvant therapy(NAT). Methods This retrospective study analyzed the clinicopathological data of 308 breast cancer patients with pathologically confirmed HER2-positive status (HER2 3+ or HER2 2+/FISH+) who received NAT combined with targeted therapy at our hospital from January 2017 to December 2020. The primary observation indicators were pCR rate and disease-free survival (DFS). Results The pCR rate in the HER2 3+ group (252 patients, 81.8%) was significantly higher than that in the HER2 2+/FISH+ group (56 patients, 18.2%) (52.4% vs . 28.6%, P