ERBB2 and breast cancer: The five are: (1) Oncotype Dx® and MammaPrint® gene expression testing for breast cancer recurrence; (2) human epidermal growth factor receptor type 2 (HER2) in breast cancer (BrCa); (3) EGFR mutation testing in non-small cell lung cancer (NSCLC); (4) KRAS mutation testing in colorectal cancer (CRC); and (5) BCR-ABL monitoring testing in chronic myeloid leukaemia (CML).