ERBB2 and neoplasm: The nanobody 225Ac-DOTA-2Rs15d showed in vitro and in vivo a higher binding efficiency to HER2-overexpressing SKOV-3 cells than to low HER2-expressing MDA-MB-231 cells (4.01% ID/g vs. 0.49% ID/g after 2 h), indicating specific binding to the antigen and resulting in high tumor to normal tissue ratios.