Whether HER2 IHC assays other than PATHWAY HER2 (4B5) can be used to identify subsets of breast cancer cases with lower levels of HER2 expression, who are candidates for treatment with T-DXd, requires further investigation, although studies have found HER2-low prevalence to be similar, regardless of assay used [20–22]. This evidence concerns the gene ERBB2 and breast carcinoma.