Ki-67 Index Provides Long-Term Survival Information for Early-Stage HER2-Low-Positive Breast Cancer: A Single-Institute Retrospective Analysis

which permits unrestricted use, distribution, and reproduction any medium, provided the original work is properly cited. Aim. It has been reported that more than half of breast cancer (BC) could be identified as HER2-low-positive, which might be a distinct subtype. But the results are controversial. We aim to compare the survival outcomes between HER2-low-positive and HER2-0 BC with Asian women based on HR status or Ki-67 index. Methods. Between January 2009 and December 2017, HER2nonamplified BC in our single institute was identified. Patients were classified as HER2-low and HER2-0 cohort. Clinical characteristics were compared between these two groups and survival outcomes were calculated by the Kaplan-Meier method. We also performed subgroup analysis according to Ki-67 index and hormone-receptor (HR) status. Results. Of the 2,230 included patients, 536 presented with HER2-0, and 1,694 with HER2-low positive. After a median follow-up of 85 months (range: 1-152 months), the 8-year OS, BCSS, and RFS of the overall cohort were 91%, 95%, and 89%, respectively. In comparison with the HER20 cohort, majority of HER2-low-expression BC concurrently presented with HR positive (82.3% vs. 69%, P < 0.001). There was no significant survival difference between the two groups in terms of OS, BCSS, and RFS (all p > 0.05). We then performed subgroup analysis according to HR status and Ki-67 index (< 14% vs. >= 14%). Our results indicated that there was no significant survival difference between HER2-low-positive and HER2-0 tumors regardless of HR status (p > 0.05), while OS (p = 0.026) and BCSS (p = 0.052) of HER2-0 BC with high Ki-67 index were significantly poorer than that of HER2-low positive with high Ki-67, but not for RFS (p = 0.17). Conclusion. Among early stage HER2-nonamplified BC, no significant survival difference could be found between HER2-low positive and HER2-0 cohort regardless of HR status. Survival outcomes of HER2-low positive with high Ki-67 seem to be poorer than that of HER2-0 tumors with high Ki-67 index.

Automated summary

This study aimed to compare the survival outcomes between HER2-low-positive and HER2-0 breast cancer, regardless of hormone-receptor (HR) status, in Asian women. The results showed no significant survival difference between the two groups, but high Ki-67 index was associated with poorer survival outcomes in HER2-0 breast cancer.