Efficacy and safety of disitamab vedotin (RC48) in HER2-expressing breast cancer: A multicenter retrospective study.

Abstract

e13011 Background: RC48 is an Antibody-Drug Conjugate (ADC) that integrates a humanized monoclonal antibody targeting human epidermal growth factor receptor 2 (HER2) linked to the microtubule inhibitor monomethyl auristatin E (MMAE). This study reports real-world data using RC48 monotherapy in HER2-expressing advanced breast cancer (ABC). Methods: The study reviewed patients with HER2-expressing ABC who received RC48 monotherapy at three hospitals in China between September 2021 and June 2022. The electronic medical record was used to collect the clinical characteristics of the patient and to evaluate the antitumor activity and safety. The primary outcome was real-world progression-free survival (rwPFS). Results: A total of 15 patients were included, of whom 9(60%) were HER2-positive and 6(40%) had HER2 low expression (IHC 1+ or IHC 2+/ISH-).11 patients (73.3%) had visceral metastases, 40% of patients (6/15) had central nervous system (CNS) metastases at baseline. 6 patients (40%) had ≥3 metastatic lesions, and 13(86.7%) of patients received RC48 as third-line treatment or higher. Progression-free survival (PFS), overall survival (OS), and response can be assessed in all patients. The median follow-up was 10 months and the median rwPFS was 8.0 months (95% CI, 4.897-11.103), while the median OS was not reached. Objective response rate (ORR) and disease control rate (DCR) were 46.7% and 80% respectively. Partial response (PR) was achieved in 46.7% of the patients (7/15). patients with HER2-positive and HER2 low expression, the median rwPFS was 8.77 and 4.63 months, respectively (HR = 0.49,95% Cl, 0.13-1.80, P = 0.196), and in 6 patients with CNS metastases, the median rwPFS was 7.5 months (95% CI, 2.82-18.28). The most common treatment-related adverse events (TRAEs) were elevated transaminase (33.3%) and Leukopenia (33.3%), most of which were grade 1-2, No serious adverse events related to treatment were observed. Conclusions: The novel HER2-targeted ADC, RC48, demonstrated promising preliminary antitumor activity in patients with HER2-expressing ABC, patient with brain metastases could also benefit, with tolerable toxicities.