The Oncotype DX Breast Recurrence Score® assay (Exact Sciences Corporation, Madison, WI, USA) is a 21-gene breast cancer assay for women with hormone receptor-positive (HR+), HER2-negative (HER2−) breast cancer which returns a Recurrence Score (RS) result of between 0 and 100. The gene discussed is ERBB2; the disease is breast carcinoma.