To study peptide distribution and accumulation in solid tumors, we choose to study GRPr-targeting radiopeptides that bind with high affinity to GRPr-expressing tumor cells It has been shown in several prostate cancers and in PDX models of prostate cancer that the GRPr expression is high [9, 11, 13, 20, 21]. Here, GRPR is linked to Familial prostate cancer.