Even if there is a limited number of synthetic antagonists, the molecules RC-3940-II (Hca6,Leu13Ψ(CH2-N)Tac14-bombesin(6-14)], RC-3950-II [d-Phe6,Leu13Ψ(CH2-N)Tac14-bombesin(6-14)) and RC-3095 (Figure 10), which all encompass the bombesin fragment Asn–Gln–Trp–Ala–Val–Gly–His–Leu–Met (residues 6–14), have been shown to decrease the volume of breast cancer xenografts, thus opening new perspectives for the treatment of breast tumors [234,235,236]. Here, GRP is linked to breast cancer.