Abstract 16P
Background
HER2-low breast cancer (BC) has become a new disease entity after approval of trastuzumab deruxtecan in HER2-low metastatic BC. However, the clinicopathological factors and prognostic outcomes of this subgroup remain unclear especially in Thai population. Therefore, our study was aimed to investigate the prognostic significance of HER2-low early-stage BC in Thai population in term of clinicopathological characteristics and survival outcomes between HER2-low and HER2-IHC 0 BC.
Methods
Patients with early-stage BC who had HER2-low (IHC 1+ or IHC 2+/ISH-) or HER2-IHC 0 and received treatment at King Chulalongkorn Memorial Hospital KCMH) between January 1, 2016 and December 31, 2017, were retrospectively reviewed. Clinicopathologic features and survival outcome between HER2 low and HER2 IHC 0 were evaluated. The primary endpoint was invasive disease-free survival (iDFS), and secondary endpoints were overall survival (OS), locoregional recurrence, distant metastasis, and second primary malignancy between two groups.
Results
Among 585 patients, 500 were HR-positive while 85 were HR positive BC. Three hundred and thirty-eight (57.8%) had HER2 low disease and 247 (42.2%) had HER2 IHC 0. 307 out of 338 patients (91.1%) in HER2 low group were classified in HR positive while only 193 out of 247 patients (78.1%) in HER2 IHC 0 showed HR positive. No differences in clinical characteristics between the HER2-low and HER2-IHC 0 group was reported in overall population. However, in the HR-positive cohort, we found differences in histological subtype between both groups (p = 0.01). With a median follow-up of 82.7 months (Range 0.7-102.8 months), the 5-year iDFS rates were 89.6% for the HER2-low group and 88.6% for the HER2-IHC 0 group (HRs (95% CI) = 0.96 (0.56-1.65), p = 0.90). In the HR-negative cohort, the 5-year iDFS rates between the two groups were 80.6% and 87.0%, respectively (HRs (95% CI) = 1.86 (0.53-6.43), p = 0.31).
Conclusions
HER2-low early-stage breast cancer is associated with difference subtype in HR-positive group, but this does not translate into survival outcomes. However, further studies with larger sample sizes are necessary to confirm the clinical significance of HER2-low breast cancer patients.
Clinical trial identification
Editorial acknowledgement
Legal entity responsible for the study
The authors.
Funding
Has not received any funding.
Disclosure
All authors have declared no conflicts of interest.