Due to its iodide concentrating ability, NIS expression in nonthyroidal tumor cells induced by targeted gene transfer enables non-invasive tumor monitoring and exact localization of the tumorous tissue by various imaging modalities (y-camera, PET, SPECT) and tracers (123I, 188Re, 124I, 18F-TFB, 18F-SO4) before therapeutic radionuclide application (131I, 188Re, 211At). The gene discussed is SLC5A5; the disease is neoplasm.