Differences of HER2 Status by HercepTest and PATHWAY 4B5 Immunohistochemical Assays in Breast Cancer | Synapse
February 2, 2026
Differences of HER2 Status by HercepTest and PATHWAY 4B5 Immunohistochemical Assays in Breast Cancer
Key Points
The aim is to compare HER2 status measurements between two immunohistochemical assays in breast cancer.
Compared HER2 staining using HercepTest and PATHWAY 4B5 assays.
Analyzed results to evaluate discrepancies in HER2 levels.
Examined implications for treatment decisions regarding T-DXd.
HER2 staining was found to be lower in the 4B5 assay compared to the HercepTest.
Differences in HER2 status may impact treatment decisions for patients with HER2-ultralow evaluations.
Abstract
HER2 staining was lower in 4B5 testing than in the HercepTest. Companion diagnosis using 4B5 is required to determine indications for T-DXd, especially for HER2-ultralow evaluations.