Oncotype Dx (Genomic Health, Redwood City, California) is a commercially available multigene reverse transcription polymerase chain reaction (RT-PCR) assay that is used to quantify the risk of distant recurrence and predict the benefits of chemotherapy in patients with stage I or II estrogen receptor positive (ER+), Her2 negative, and lymph node negative (LN−) invasive breast cancer treated with tamoxifen [1]. This evidence concerns the gene ESR1 and invasive breast carcinoma.