Abstract 295P
Background
About 50% of BC presented with a HER2-low expression, defined as HER2 immunohistochemistry score of 1+ or 2+ with negative in situ hybridization assay. No anti-HER2 agents are currently approved in Europe for this subgroup, nevertheless new antibody-drug conjugate showed meaningful activity. This study aimed to investigate the clinical relevance of HER2-low status as a independent prognostic factor in mBC and its potential utility in predictive 1L outcome.
Methods
A retrospective analysis was conducted on a consecutive series of 322 luminal mBC patients (pts) without Her2 iperexpression, receiving 1L endocrine therapy (ET) or ET in combination with a CDKi (ET+CDKi) at the Oncology Department of Udine and Aviano (Italy) from 2008 to 2019. Association analysis were investigated through Fisher-exact test. The prognostic impact of HER2-low was investigated through Cox regression, and differences in progression free survival (PFS) and overall survival (OS) were tested by log-rank.
Results
In the total series, 247 pts (63.8%) were aged >65, 88.1% was post-menopausal, 34.3% had de novo metastatic disease, 37.7% had visceral disease, 23% had ≥3 sites of involvement. As 1L, 238 pts (73.9%) received ET while 84 pts (26.1%) were treated with ET+CDKi. As expected, in the total series HER2-negative (i.e. HER2 score 0) BC were 212 (65.8%) while HER2-low were 110 (34.2%), no association with visceral disease, number of sites of disease, and menopausal status was detected (p>0.05). By univariate analysis, HER2-low was not associated with prognosis neither in terms of PFS (HR 0.98, P=0.91, 95% CI 0.76-1.26) nor OS (HR 1.01, P=0.932, 95% CI 0.76-1.34). Interestingly, in the subgroup of pts treated with ET+CDKi, HER2-low had no statistically significant impact on PFS (HR 0.98, P=0.96, 95% CI 0.55-1.76) or OS (HR 0.89, P=0.79, 95% CI 0.38-2.10), similarly in the population treated with ET (PFS: HR 0.98, P=0.94, 95% CI 0.74-1.31 and OS: HR 1.04, P=0.79, 95% CI 0.76-1.41).
Conclusions
In the present exploratory study, pts with HER2-low and HER2 negative luminal mBC showed a comparable outcome when treated with ET or ET+CDK4/6i. Further prospective studies are needed to explore this novel subgroup.
Clinical trial identification
Editorial acknowledgement
Legal entity responsible for the study
Azienda Sanitaria Universitaria Friuli Centrale (ASUFC).
Funding
Has not received any funding.
Disclosure
All authors have declared no conflicts of interest.