The 21-gene recurrence score (RS) assay (Oncotype DxTM, Genomic Health, Redwood City, CA) is the most used prognostic assay in the United States, recommended by National Comprehensive Cancer Network and the American Society of Clinical Oncology for patients with early stage, estrogen receptor (ER)-positive, HER2-negative breast cancer [6]. Here, ERBB2 is linked to breast cancer.