CXCR4 and breast cancer: In prostate and breast cancer alone, more than ten GPCRs have been implicated, with the most prominent associations seen for Cys-X-Cys Chemokine Receptor 4 (CXCR4), G protein-Coupled Receptor 19, Lysophosphatidic receptor 6, Protease Activated Receptor 1 and 2 (PAR-1 and -2), Prostaglandin E2 (PGE2) and Cholinergic Receptor, Muscarinic 1 [3].