Inherent issues of subjectivity and inconsistency have long plagued immunohistochemistry (IHC)-based Her2 assessment, leading to the repeated issuance of guidelines by the American Society of Clinical Oncology/College of American Pathologists (ASCO/CAP) for its standardization for
breast cancer patients. Yet, all these efforts may prove insufficient with the advent of
Trastuzumab deruxtecan (T-Dxd), a
drug with the promise to expand to
tumors traditionally defined as Her2 negative (Her2-). In this study, we attempted to address these issues by exploring an ELISA-like quantitative dot blot (
QDB) method as an alternative to IHC. The
QDB method has been used to measure multiple
protein biomarkers including ER, PR, Ki67, and
cyclin D1 in
breast cancer specimens. Using an independent cohort (cohort 2) of
breast cancer formalin-fixed
paraffin-embedded (FFPE) specimens, we validated cutoffs developed in cohort 1 (Yu et al., Scientific Reports 2020 10:10502) with overall 100% specificity (95% CI: 100-100) and 97.56% sensitivity (95% CI: 92.68-100) in cohort 2 against standard practice with the dichotomized absolutely quantitated values. Using the limit of detection (LOD) of the
QDB method as the putative cutoff point,
tumors with no Her2 expression were identified with the number comparable to those of IHC 0. Our results support further evaluation of the
QDB method as an alternative to IHC to meet the emerging need of identifying
tumors with low Her2 expression (Her2-low) in daily clinical practice.