434P - Incidence and prognostic value of HER2-low expression metastatic breast cancer in Asian population: A 10-year retrospective study

Background

The natural disease across each molecular subtype of breast cancer are variable. Although novel drugs for the treatment of human epidermal growth receptor (HER2) overexpression subtype metastatic breast cancer have been widely utilized, the treatment options for HER2 low expression is limited. The epidemiology and clinical outcome of metastatic HER2-low expression breast cancer among the Asian population have not been thoroughly described.

Methods

A 10-year retrospective cohort study was conducted from the Ramathibodi Cancer Registry database during 2011-2021. We aimed to investigate the incidence and compare the overall survival (OS) of non-HER2 expression and HER2-low metastatic breast cancer. Prognostic factors for survival were analyzed by logistic regression analysis.

Results

Out of 8,633 patients, 491 met the study criteria. Of those, 104 (21.2%) had HER2-low expression tumors, while 247 (50.3%) had HER2-negative expression tumors. When stratified by hormonal receptor status, 85 patients (81.7%) were hormonal receptor (HR)-positive and 19 patients (18.3%) were HR-negative. The median OS (IQR) was significantly longer in patients with HER2-low expression tumors compared to those with HER2-negative expression tumors (median OS 41 (26-56) months vs. 23 (19-27) months; HR, 0.66, 95% CI (0.49-0.88), p = 0.004). Among the HR-positive tumors, patients with HER2-low expression also had a significantly longer OS than those without HER2 expression (median OS 54 (42-66) months vs. 30 (26-34) months; HR, 0.65, 95% CI (0.46–0.92), p= 0.014). In the HR-negative group, the survival in patients with HER2-low expression tumors was comparable to those without HER2 expression tumors (median OS 13 (8-18) months vs. 14 (11-17) months; HR, 1.09, 95% CI (0.64–1.86), p=0.76).

Conclusions

One in five Asian patients with metastatic breast cancer could develop HER2 low-expression tumors. Those with HER2 low-expression tumors, particularly in the HR-positive subtype, tend to have longer survival than those without HER2 expression tumors among patients with metastatic breast cancer.

Clinical trial identification

Editorial acknowledgement

The authors would like to thank Ramathibodi Cancer Registry Unit of Ramathibodi Comprehensive Cancer Center for the support of clinical data.

Legal entity responsible for the study

The authors.

Funding

Has not received any funding.

Disclosure

All authors have declared no conflicts of interest.