A meta-analysis of the difference in response to trastuzumab-deruxtecan (T-DXd) based on HER2 immunohistochemistry (IHC) in HER2 low metastatic breast cancer (mBC).

Abstract

e13164 Background: HER2 low BC have an IHC staining of 1+ or 2+ with negative fluorescence in situ hybridization (ISH). Although T-DXd is approved for this, difference in activity between 1+ and 2+ is uncertain. Methods: A systematic search with controlled vocabulary encompassing BC and T-DXd was conducted in PubMed, Embase, Scopus, and Cochrane on November 11 2023 with no search restrictions. 2318 records were identified and duplicates were removed using Mendeley. The remaining 1189 records were imported into Rayyan, and the titles were screened independently by 2 reviewers. 47/75 full texts were relevant, of which 4 [3 clinical trials, 1 retrospective study] were included for analysis. Only studies that provided outcome data for HER2 1+ and 2+ ISH- were included. RevMan was used to analyze the Risk Ratio (RR) and Odds Ratio (OR) with 95% Confidence Interval (CI), derived from Random Effects (RE) model with Mantel-Haenszel (MH) method. Pooled proportions (PP) were determined using OpenMeta. Results: There were a total of 264 patients in 1+ and 204 in 2+ISH-. Median age was 57 years. All studies had pre-treated mBC. T-DXd dose was at least 5.4 mg/kg every 3 weeks. Visual inspection of our funnel plots revealed no bias. PP (3/4 studies) for patients achieving an Objective Response Rate (ORR) [Complete Response (CR)+Partial Response (PR)] was 42.9% (31.6-54.2%) in 1+ and 38% (26.3-49.7%) in 2+. The median Progression free survival (2/4 studies) was 8.6 (1+) and 7.95 (2+) months respectively. RE RR (3/4 studies) for Progressive Disease (PD) showed no difference between 1+ and 2+ [0.93 (0.80, 1.10), p=0.4, I²=0%]. Similarly, RE OR (3/4 studies) for Disease Control Rate (DCR) [CR+PR+Stable disease (SD)] [1.20 (0.78, 1.85), p=0.41, I²=0%], ORR [1.17 (0.58, 2.34), p=0.66, I²=0%], and PR [1.05 (0.52, 2.11), p=0.89, I²=0%] showed no significant difference between 1+ and 2+ (Table). Conclusions: Our results indicate no difference in response to T-DXd between 1+ and 2+, solidifying its role as a treatment option in HER2 low mBC. Limited number and heterogeneity between studies are limitations of our study, which ought to be addressed in future trials through clear subgroup stratification between 1+ and 2+. [Table: see text]