SLC5A5 and neoplasm: NIS-specificity of [18F]BF4− uptake was demonstrated in vivo by the following observations: first, there was no significant tracer uptake in non-NIS expressing primary tumors (3E.Δ) (Fig. 2a) and second, administration of ClO4− before radiotracer administration in a repeat scan of 3E.Δ-NIS tumor-bearing animals abolished uptake in primary tumors and all endogenous NIS-expressing organs (Fig. 2b).