Investigation of the Effect of Low-positive HER-2 on Neoadjuvant Chemotherapy Response in Hormone-positive Breast Cancer Patients

Objective: Recently, it has been suggested that low-positive human epidermal growth factor receptor-2 (HER-2) is a separate group of breast cancer. We examined the effect of low-positive HER-2 on neoadjuvant chemotherapy (NACT). Methods: This retrospective study included female patients aged >18 years who were diagnosed with histologically proven breast cancer between January 1, 2016, and January 1, 2020, and had breast surgery after NACT. Patients with triple-negative, estrogen receptor (<10%) weak positive, HER-2 immunohistochemical (IHC) scores 3+ or 2+/FISH-positive patients, and metastatic patients were excluded. Pathological complete response (pCR) was defined as the no invasive and in situ residue in the breast and lymph nodes in surgery after NACT. Results: One hundred twenty seven patients were included in this study. HER-2 IHC-score “0” patients were 55 (43.3%), “1+” patients were 52 (40.9%), and “2+” patients were 20 (15.7%). Nine (7.1%) patients showed a complete response to NACT. In the univariate analysis with clinicopathological variables of the patients to predict the complete response to NACT; estrogen receptor [odds ratio (OR): 0.97, 95% confidence interval (CI): 0.96-0.99, p=0.012], Ki-67 (OR: 1.12, 95% CI: 1.06-1.18, p<0.001), tumor grade (OR: 0.036, 95% CI: 1.13-30.36, p=0.036), and lymphovascular invasion (OR: 0.11, 95% CI: 0.01-0.93, p=0.043) showed the predictive features. In the multivariate analysis, Ki-67 (OR: 1.10, 95% CI: 0.04-1.17, p=0.001) was found to be an independent predictor of pCR. Conclusion: We determined that the low-positive-HER2 group has no effect on the treatment response in patients treated with NACT. We found that Ki-67 was an independent predictive for pCR.