Ergun, Yakup; Ucar, Gokhan; Akagunduz, Baran

Background: The prognostic differences between HER2-zero and HER2-low breast cancer (BC) remain unclear. Purpose of this meta-analysis is to investigate the differences between HER2-low and HER2-zero in terms of clinicopathological factors and survival outcomes in early-stage BC. Methods: We searched major databases and congress proceedings until November 1, 2022 to identify studies comparing HER2-zero and HER2-low in early-stage BC. HER2-zero immunohistochemically (IHC) was defined as score 0, while HER2-low was defined as IHC 1+ or 2+/in situ hybridization negative. Result: A total of 23 retrospective studies involving 636,535 patients were included. HER2-low rate was 67.5% in the hormone receptor (HR)-positive group, while this rate was 48.6% in the HR-negative group. In the analysis of clinicopathological factors by HR status, the proportion of premenopausal patients within the HR-positive group was greater in the HER2-zero arm (66.5% vs 61.8%), whereas grade 3 tumors (74.2% vs 71.5%), patients younger than 50 years of age (47.3% vs 39.6%), and T3-T4 tumors (7.7% vs 6.3%) within the HR-negative group was higher in the HER2-zero arm. In both the HR-positive and HR-negative groups, the HER2-low arm showed significantly improved results for disease-free survival (DFS) and overall survival (OS). The hazard ratios for DFS and OS in the HR-positive group were 0.88 (95% CI 0.83–0.94) and 0.87 (95% CI 0.78–0.96), respectively. In the HR-negative group, the hazard ratios for DFS and OS were 0.87 (95% CI 0.79–0.97) and 0.86 (95% CI 0.84–0.89), respectively. Conclusion: In early-stage BC, HER2-low is associated with better DFS and OS compared to HER2-zero, regardless of HR status.