Conclusions: The present study showed that increase of PEG-spacer length in the [99mTc]Tc-DB7–[99mTc]Tc-DB13–[99mTc]Tc-DB14 series had little effect on GRPR affinity, specific uptake in PC-3 cells, in vivo stability, or tumor uptake. The gene discussed is GRPR; the disease is neoplasm.