RTN4R and digestive system neoplasm: The tumor/blood, tumor/lung, tumor/heart, tumor/liver, tumor/spleen, tumor/kidney, tumor/stomach, tumor/intestine, tumor/pancreas, tumor/brain, tumor/bone and tumor/muscle ratios of NGR-hPK5 were all significantly higher (p<0.05) than those of hPK5 at 1 h and 6 h.