Although smaller-sized anti-HER2 immune fragments, such as F(ab’)212, F(ab’)13, single-chain variable fragment (scFv)14, single domain antibody fragment15, and affibody molecules16, could enable high-contrast PET imaging at the target site at earlier time (i.e., 2–3 h post-injection (p.i.)), and with better tumor tissue penetration, this is generally precluded due to their typically shorter blood circulation half-lives (minutes to hours) and faster whole-body clearance rates. The gene discussed is ERBB2; the disease is neoplasm.