CXCR4 and small cell lung carcinoma: For this purpose, radiolabeled probes are used that target, for example, enzyme activities, transport systems, and surface receptors with high affinity and specificity.[6–8] We describe the development of the first gallium-68 (t1/2=68 min) ligand for the G-protein-coupled receptor CXCR4 and preliminary demonstrate its potential for in vivo imaging of CXCR4 expression using a mouse model with a human small-cell lung cancer xenograft.