Abstract 140P
Background
In this study, we have compared the clinicopathologic characteristics of HER2-low breast cancer to HER2-zero and HER2-positive breast cancer, including response to neoadjuvant chemotherapy and prognosis.
Methods
Patients who underwent neoadjuvant chemotherapy between 2008 and 2018 at Asan Medical Center were included in this study. HER2-low was defined as immunohistochemistry (IHC) 1+ or IHC2+/in-situ hybridization negative and HER2-zero was defined as IHC 0.
Results
A total of 1667 breast cancer patients who had neoadjuvant chemotherapy were included in this study. Among them 474 (28.4%) patients had a HER2-low tumor, 677 (40.6%) patients with a HER2-zero tumor and 516 (31.0%) patients with a HER2-positive tumor. The proportion of HER2-low tumors was higher in hormone receptor (HR)-positive patients compared to triple-negative breast cancer (TNBC) patients (49.5% vs 28.9%, respectively). HER2-low tumors had a significantly lower pCR rate compared to HER2-zero tumors (11% vs 15.4%, p=0.04). pCR rate was also significantly lower in HER2-low tumors compared to patients with HER2-positive tumors who were not treated with neoadjuvant HER2-targeted therapy (11% vs 17.4%, p=0.008). However, pCR rates did not differ according to HER2 status in HR-positive subgroups or TNBC subgroups. Patients with HER2-low tumors had significantly longer survival compared to patients with HER2-zero tumors (5-year RFS 78.8% vs 73.3%, log-rank test p=0.017; 5-year OS 90.8% vs 84.0%, log-rank test p=0.005). Survival differences were seen in patients with TNBC tumors (5-year RFS 73.5% vs 64.8%, log-rank test p=0.034), but not in patients with HR-positive tumors (5-year RFS 80.8% vs 81.5%, log-rank test p=0.87). Survival difference according to HER2-low status was only identified in TNBC patients with non-pCR, whereas no difference was noticed in TNBC patients with pCR (5-year RFS: low/pCR 92.7%, zero/pCR 90.0%, low/non-pCR 68.6%, zero/non-pCR 56.7%; log-rank test p<0.001).
Conclusions
HER2-low tumors have a distinct biology presenting with lower pCR but longer survival rate compared to patients with HER2-zero tumors. These results suggest a need for better understanding of the biology of HER2-low tumors and the refinement of future therapeutic strategies.
Legal entity responsible for the study
The authors.
Funding
Has not received any funding.
Disclosure
All authors have declared no conflicts of interest.