Impact of Hormone Receptor Status and HER2 Expression on Neoadjuvant Targeted Therapy Response in HER2-Positive...

Previous studies indicate that HER2 protein expression and hormone receptor (HoR) status affect the sensitivity of HER2-positive breast cancer to neoadjuvant therapy, but it is unclear if sensitivity varies among subgroups defined by HER2 and HoR status. We examined 2 cohorts of patients, aged 18 to 80 years, with HER2-positive early breast cancer who underwent neoadjuvant therapy followed by surgery between January 1, 2009, and December 31, 2022: cohort 1 included 2648 patients, and cohort 2 had 141 patients with RNA expression data. Patients were divided into 4 groups based on immunohistochemical HER2 and HoR status: HER2(3+)/HoR-, HER2(3+)/HoR+, HER2(2+)/HoR-, and HER2(2+)/HoR+. We evaluated total pathological complete response (TpCR, defined as ypT0/is ypN0) rates, disease-free survival (DFS), and variations in PAM50 intrinsic subtypes across different subgroups. In cohort 1, HER2(3+)/HoR- had a higher TpCR rate (44.5%) than HER2(3+)/HoR+ (33.8%) (P < .001), HER2(2+)/HoR- (31.7%) (P = .013), and HER2(2+)/HoR+ (13.8%) (P < .001). DFS was similar across groups (P = .445). Trastuzumab or trastuzumab plus pertuzumab significantly improved TpCR rates and DFS in HER2(3+)/HoR- and HER2(3+)/HoR+ but not in HER2(2+)/HoR- and HER2(2+)/HoR+. Cohort 2 showed significant PAM50 subtype differences across these groups (P < .001). In conclusion, the responsiveness of HER2-positive breast cancer to neoadjuvant targeted therapy is significantly influenced by HER2 expression levels and HoR status, emphasizing the necessity of precision medicine approaches to tailor therapeutic strategies for improved clinical outcomes.