The tumor uptake of [203Pb]Pb-PSC-PEG2-TOC was almost completely blocked by co-administration of excessive unlabeled peptide, indicating that the high tumor uptake of [203Pb]Pb-PSC-PEG2-TOC is mediated by specific binding to SSTR2 (Fig. 4a, c). Here, SSTR2 is linked to neoplasm.