429P - The impact of HER2 status on the efficacy of CDK 4/6 inhibitors: A multicenter study

Background

The prognostic significance of Human Epidermal Growth Factor Receptor 2 (HER2)-low status in patients with hormone receptor-positive (HR+)/HER2-negative advanced breast cancer (aBC) who receive first-line endocrine therapy combined with cyclin-dependent kinase (CDK) 4/6 inhibitors remains uncertain. Two major studies in this area have yielded conflicting results, indicating the need for further research. Therefore, Our objective is to examine the effect of HER2 status on overall survival (OS) outcomes among patients who are undergoing first-line treatment with CDK 4/6 inhibitors.

Methods

Our study is a multi-center, retrospective, real-world data analysis focusing on patients diagnosed with hormone receptor-positive, HER2-negative metastatic breast cancer who were treated with CDK 4/6 inhibitors as first-line therapy.

Results

Our study included 160 patients from five tertiary hospitals. The median follow-up time was 19.90 ± 0.82 months, and mOS could not be reached. Of the patients, 83 were included with recurrent metastatic disease. 118 were postmenopausal. 63 patients were treated with palbociclib and 97 were treated with ribociclib. 111 had HER2 negative and 49 had HER2 low status. The median overall survival in the HER2 low group was 49.03 months, while the mOS could not be reached in the HER2-negative group (HR: 0.87, p=0.818). There was no difference in OS between patients treated with palbociclib and ribociclib (p=0.416).

Conclusions

Our study is one of the few with a large sample size, examining the relationship between CDK 4/6 inhibitors' efficacy and HER2 status. Previous research includes two studies with a high number of patients and three with a low number of patients, with inconsistent results in the two larger studies. In our study, which included a significant number of patients, we showed that CDK 4/6 inhibitors had a similar overall survival in the HER2 low group and the HER2-negative group. In our study, there was no significant difference in overall survival between the use of palbociclib and ribociclib.

Clinical trial identification

Editorial acknowledgement

Legal entity responsible for the study

Hacettepe University Ethics Boards and Commissions.

Funding

Has not received any funding.

Disclosure

All authors have declared no conflicts of interest.