Abstract
INTRODUCTION: Human epidermal growth factor receptor 2 (HER2)-targeted therapies have shown effectiveness against HER2-positive breast cancer. This makes neoadjuvant chemotherapy (NAC) a valuable option for treating both early and advanced stages of the disease. The tumor's response to HER2-targeted NAC provides crucial prognostic information. Additionally, it allows for tailoring adjuvant treatment strategies for HER2+ breast cancer based on pathological responses. This study aimed to investigate the clinicopathological factors that influence tumor response. METHODS: We retrospectively analyzed 122 patients diagnosed with HER2+ breast cancer. These patients received NAC and HER2-directed therapy between January 2018 and December 2022 at the Pusan National University Yangsan Hospital. Following surgery, tumor response was evaluated, categorizing patients into two groups: pathological complete response (pCR) and non-pCR groups. We analyzed data on various factors, including age, NAC regimen, type of breast and axillary surgery, clinical stage (cTNM), historical grade, and preoperative levels of carcinoembryonic antigen, cancer antigen 15-3 (CA 15-3), estrogen receptor (ER), progesterone receptor (PR), HER2, p53, and KI-67. RESULTS: Out of the 122 patients, 75 achieved pCR, while 47 did not. Most clinicopathological factors showed no significant difference between the pCR and non-pCR groups. However, several factors were associated with a higher pCR rate: normal preoperative CA 15-3 levels (odds ratio [OR]: 3.74, confidence interval [CI]: 1.19-11.72, p = 0.02), preoperative ER positivity (OR: 2.65, CI: 1.25-5.59, p = 0.01), PR negativity (OR: 3.92, CI: 1.82-8.45, p < 0.05), and strong preoperative HER2 immunohistochemistry (IHC) 3+ staining. Multivariate analysis confirmed that PR negativity (OR: 2.8, CI: 1.23-6.42, p = 0.01) and strong preoperative HER2 IHC 3+ staining (OR: 0.18, CI: 0.03-0.84, p = 0.04) were independent predictors of a higher pCR rate. CONCLUSIONS: A pCR after NAC impacts patient prognosis and influences the choice of adjuvant treatment for HER2+ breast cancer. Clinicopathological factors can help predict responses to HER2-targeted NAC. In our study, pre-ER/PR negativity, high pre-HER2 levels, and normal CA 15-3 levels were found to be potential predictors of pCR. These findings may contribute to developing more effective treatment strategies for HER2+ breast cancer.