ERBB2 and neoplasm: Gold nanoparticles coated with PEG and conjugated with anti-HER2 trastuzumab antibodies can be prepared with finely-tuned particle sizes for improved intratumoral distribution (15–30 nm) and led to a two-fold increase in KPL-4 xenograft tumor contrast when compared with images obtained with an iodinated small-molecule contrast agent in X-ray CT, although the majority of the accumulated dose was retained within neovascular regions of the tumor tissues (Fig. 6) (91).