K. Jin1, Z. Yang2, L. Zhang2, and X. Yu2; 1Department of Radiation Oncology, Fudan University Shanghai Cancer Center; Department of Oncology, Shanghai Medical College, Fudan University, Shanghai, China, 2Department of Radiation Oncology, Fudan University Shanghai Cancer Center; Department of Oncology, Shanghai Medical College, Fudan University; Shanghai Clinical Research Center for Radiation Oncology; Shanghai Key Laboratory of Radiation Oncology, Shanghai, China
Purpose/Objective(s): HER2-low breast cancer patients have been benefited from novel anti-HER2 antibody-drug conjugates (ADCs). However, the characteristics of HER2-low breast cancer are not well understood, especially the prognostic value of HER2-low in locoregional recurrence (LRR) rates. The current study is to compare the LRR rates and survival outcomes between HER2-low and HER2-zero patients after surgery and adjuvant radiotherapy. Materials/
Methods: We retrospectively reviewed the consecutive HER2-low and HER2-zero breast cancer patients between 2012 and 2018. All the patients underwent radical breast surgery and postoperative radiotherapy. The target volume included breast/chestwall and regional node area. Kaplan–Meier analysis and Cox regression were used to assess the LRR-free survival (LRRFS), distant metastasis-free survival (DMFS) and overall survival (OS). Results: A total of 2143 patients were included, of whom 1400 patients were identified as HER2-low. Compared with HER2-zero patients, HER2-low patients exhibited lower tumor grade and higher ER positivity. The 5-year LRRFS for HER2-low and HER2-zero cohorts were 96.8% and 95.8%, respectively (p=0.203). No differences were observed in terms of LRR pattern between HER2-low and HER2-zero patients. In ER+ cohort, HER2-low patients demonstrated significantly improved LRRFS (HR 0.42, 95% CI 0.20-0.89, p=0.024) and borderline improved DMFS (HR 0.73, 95% CI 0.52-1.02, p=0.064) compared with HER2-zero patients in multivariate analysis. However, in ER- cohort, no significant differences were observed between HER2-low and HER2-zero patients in either LRRFS or DMFS. No prognostic value of HER2-low was found with regard to OS in both ER+ and ER- cohorts. Conclusion: This study explored the LRR pattern in HER2-low breast cancer patients and HER2-low might be a prognostic factor for LRR in ER+ patients after surgery and postoperative radiotherapy. However, the prognostic value of HER2-low status still warranting further research.
