The in vivo GRPR-targeting specificity study for [111In]In-AU-RM26-M1 in mice bearing PC-3 tumors (GRPR-positive) showed a significant reduction in tumor activity uptake in the GRPR-blocking group at 1 h pi (0.9 ± 0.6%IA/g vs. 7.0 ± 0.7%IA/g for controls; p < 0.001, n = 4). The gene discussed is GRPR; the disease is neoplasm.