CD177 and neoplasm: Beside above enzyme-responsive probes and those smart probes responsive to tumor microenvironment stimuli (e.g., pH, pressure, etc) 25-26, there are lots of probes to label tumor cell surface receptors (e.g., biotin-biotin receptor system) 27 or endothelial cell surface receptors of tumor vessels (e.g., Arg-Gly-Asp (RGD)-αvβ3 integrin system) 28 for active tumor-targeting imaging.