ERBB2 and breast cancer: This assay analyses a panel of 21 genes in women presenting early stage ER+, HER2- breast cancer, in order to determine a ‘Recurrence Score (RS)’ [5,6,7,8,9], (scored as 0–100), corresponding to the 10-year risk of recurrence, and is used to stratify low (<18), intermediate (18–30), or high (≥31) risk groups, predicting whether the patients may benefit from adjuvant chemotherapy or not [5,6,7,8].