However, in contrast to the sometimes-pronounced CXCR4 expression observed in ex vivo immunohistochemistry studies using tumor biopsies, the corresponding in vivo [68Ga]Pentixafor PET/CT studies demonstrated a very heterogeneous, often modest, and in some cases even absent CXCR4-mediated tracer uptake in solid cancers [26,27,28,29], limiting the broad diagnostic application of this imaging approach. This evidence concerns the gene CXCR4 and neoplasm.