Patients were recruited at the Northern Centre for
Cancer Care (Newcastle upon Tyne Hospitals NHS
Foundation Trust). Key inclusion criteria for the study
were age 18 years, histological confirmation of primary
breast cancer with HER2 testing and written
voluntary informed consent. Ethics approval was obtained
from Newcastle and North Tyneside Ethics
Committee 2. A diagram indicating the procedure for
patient recruitment is included as Supplementary Fig. 1.