Multi-gene expression assays (MGAs), initially adapted microarrays as the platform interrogating whole transcriptome and then commercialized with reserve transcription-polymerase chain reaction (RT-PCR), digital RNA counting (NanoString Technologies, Inc, South Lake Union, Seattle, WA), and next-generation sequencing (NGS)-based RNA sequencing have been advocated for hormone receptor (HR)-positive and HER2-negative early breast cancers for risk stratification, and serve as a decision-making tool to avoid chemotherapy. This evidence concerns the gene ERBB2 and breast carcinoma.