Clinicopathological Predictors of Axillary Pathological Complete Response and Its Prognostic Significance in...

Background and Objectives: This study aimed to identify clinicopathological factors associated with axillary pathological complete response (ApCR) in patients with HER2-positive breast cancer presenting with clinically node-positive disease (cN+) confirmed by biopsy who received neoadjuvant therapy (NAT), and to assess the prognostic significance of ApCR on survival outcomes. Materials and Methods: A total of 221 patients with clinically node-positive (cN+) HER2-positive invasive breast cancer, with nodal involvement confirmed by fine-needle aspiration or core needle biopsy, who received neoadjuvant therapy (NAT) and subsequently underwent surgery at three centers between January 2015 and January 2025 were retrospectively reviewed. The association between clinicopathological factors and axillary pathological complete response (ApCR) was analyzed using logistic regression. Survival analyses were performed using the Kaplan-Meier method. Results: The median follow-up duration was 34.3 months. Axillary pathological complete response (ApCR) was achieved in 67.9% of patients. The ApCR rate was higher in stage II disease compared with stage III (76.9% vs. 62.9%). Patients with HER2 3+ tumors demonstrated a higher ApCR rate (70.8%) than those with HER2 2+/FISH+ tumors (46.2%). In multivariable logistic regression, HER2 3+ status (OR = 2.745; 95% CI: 1.138-6.619; p = 0.025) and lower clinical stage (OR = 2.251; 95% CI: 1.182-4.287; p = 0.014) were independently associated with a higher likelihood of achieving ApCR. In survival analyses, the 3-year event-free survival rate was 92% (95% CI: 86-98%) in the ApCR group, compared with 75% (95% CI: 63-87%) in the non-ApCR group. Kaplan-Meier analysis demonstrated that ApCR was a significant prognostic factor for EFS (p = 0.001). Median overall survival (OS) was not reached in either group due to the limited number of death events. Conclusions: ApCR was frequent in node-positive HER2-positive breast cancer after neoadjuvant therapy. HER2 3+ status and lower clinical stage independently predicted ApCR, which in turn was associated with improved event-free survival. These findings underscore the prognostic relevance of ApCR in this setting.