Consistent with the MC1R affinity determined in an in vitro study, [125I]NpG-GGN4b exhibited significantly higher accumulation in the tumor than [125I]NpG-GGN3b (p < 0.05) and was comparable to [111In]In-DOTA-GGNle-CycMSHhex. This evidence concerns the gene MC1R and neoplasm.