Alternative assays including RT-qPCR, FISH with alternative control probes for chromosome 17, and genomic profiling have been suggested to resolve HER2 ambiguity in 2018 ASCO/CAP ISH group 4 breast cancers.3,5–8,10 Our study included trastuzumab-treated 2018 ASCO/CAP ISH group 4 breast cancers and we attempted to assess systemic treatment patterns and disease outcome. This evidence concerns the gene ERBB2 and breast cancer.