We thank Kossatz and Notni for their interest in our article about the use of fluorescent cRGD-ZW800-1 for visualization of tumor tissue in humans during surgery (1). Their concern seems the specificity of the tracer for integrin αvβ6, which is lower than for αvβ3, and the relation with our hypothesis. The latter seems clearly defined: “Documentation of the first clinical experience with cRGD-ZW800-1, particularly in patients with colonic cancer.” The specificity of the tracer for αvβ6 was clearly of secondary importance, indicated by the absence in title and abstract. Furthermore, we have stated that the cRGD peptide is applicable for many integrins: “cRGD is a clinically well-known peptide that binds to a wide range of integrins, including αvβ1, αvβ3, αvβ5, αvβ6, and αvb8.”

Concerning the affinity of cRGD-ZW800-1: in our (pre)clinical experience, there is no “threshold” affinity for effective in vivo imaging in the complex microenvironment of a...

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