ERBB2 and neoplasm: HER2 tumour specificity was first established with [99mTc(CO)3]+-G3 DARPin-His6, which had 3.5-fold higher uptake in HER2-positive (BT474) tumours than in HER2-negative (MDA-MB-468) tumours (3.5 ± 1.1 vs. 1.0 ± 0.2 % ID/g at 24 h after administration).