Abstract 52P
Background
For trastuzumab deruxtecan (T-DXd) treatment in human epidermal growth factor receptor 2 (HER2)-low metastatic breast cancer (MBC), there are currently no real-world data to assess the efficacy differences between the immunohistochemistry (IHC) 1+ and 2+ subgroups. This study thus investigated the effectiveness and safety of T-DXd in a real-world Chinese population with HER2-low MBC and compared the outcomes between these two categories.
Methods
This single-centre, retrospective study enrolled patients with HER2-low MBC who received T-DXd between June 2022 and December 2023. The primary study endpoint was progression-free survival (PFS). Objective response rate (ORR) and clinical benefit rate (CBR) were also reported. Safety was monitored by documenting adverse events (AEs).
Results
Among the 70 eligible patients, 37 (52.9%) had IHC 1+ and 33 (47.1%) had IHC 2+. Thirty-three (47.1%) patients received ≥ 3 lines of chemotherapy before T-DXd treatment. The median initial T-DXd dose was 4.6 mg/kg (interquartile range: 3.7-5.3) every three weeks. The median PFS for the IHC 1+ and 2+ groups was 3 and 5 months, respectively (adjusted hazard ratio [HR]: 0.51, 95% confidence interval [CI]: 0.28-0.95, p = 0.034). The ORR was 16.2% and 27.3%, respectively, while the CBR was 24.3% and 36.4%, respectively. Patients who received ≥ 3 lines of previous chemotherapy had a shorter PFS compared to those who received ≤ 2 lines (median PFS: 3 vs. 5 months, adjusted HR: 1.99, 95% CI: 1.10-3.58, p = 0.022). Patients who received higher initial T-DXd doses demonstrated a better prognosis than those who received lower doses (adjusted HR: 0.64 per mg/kg, 95% CI: 0.45-0.89, p = 0.009). Nausea was the most prevalent AE, occurring in 30 (42.9%) participants, while the most common grade 3-4 AEs were neutropenia, anemia, and leukopenia (each 7.1%). No significant differences in toxicity were observed between the IHC 1+ and 2+ groups.
Conclusions
Compared to patients with IHC 1+, those with IHC 2+ are more likely to benefit from T-DXd treatment. Intensive previous chemotherapy and insufficient initial T-DXd doses might negatively impact the efficacy of T-DXd.
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.