Flow cytometry demonstrated that G3 DARPins labelled with cold indium and cold iodine bound to HER2-positive human breast cancer cells (BT474) and HER2-positive human gastrooesophageal junction (OE-19) adenocarcinoma cells, but did not bind to HER2-negative human breast adenocarcinoma cells (MDA-MB-468). The gene discussed is ERBB2; the disease is breast adenocarcinoma.