The hCXCR4- and mCXCR4-specific binding of [125I]CPCR4.3 was investigated in a panel of human and murine cancer cell lines with different levels of endogenous CXCR4 expression as well as CHO-K1 cells transiently transfected with hCXCR4 and mCXCR4 (positive controls) and compared to the hCXCR4 selective reference compound [68Ga]Pentixafor. The gene discussed is CXCR4; the disease is cancer.