Currently, National Comprehensive Cancer Network (NCCN) guidelines for breast cancer propose that multigene assays comprising 21-gene recurrence score (RS) assay (Oncotype Dx) and 70-gene signature (MammaPrint) are conductive to guiding the use of adjuvant chemotherapy in some patients with hormonal receptor (HR)-positive and HER2-negative breast cancer (10). The gene discussed is ERBB2; the disease is breast cancer.