Recruitment into groups 1 and 3 was broadly as planned to mirror the proportion of patients in the UK HER2-positive BC population receiving types of treatment that could be expected to impact productivity and HRQoL (Group 1: with chemotherapy and HER2 targeted therapy [planned n = 40/100, actual n = 27/89]; Group 3: first-line treatment [planned n = 50/100, actual n = 55/102]; Additional file 1: Table S2). This evidence concerns the gene ERBB2 and breast cancer.