Oncotype Dx is one of the most validated multigene signature assay, developed by Paik and colleagues (Paik et al., 2004) at Genomic Health, Inc. The ASCO guidelines incorporate it for the early-stage ER+/HER2−− node-negative BC patients with a high risk of recurrence Tian et al. (2008). The gene discussed is ESR1; the disease is breast cancer.