For instance, a variety of GPCRs and their ligands are involved in tumor angiogenesis, such as angiotensin (Ang) II type I receptor/AngII in breast cancer, sphingosine-1-phosphate receptor 1 (S1PR1)/sphingosine-1-phosphate (S1P) in lymphangiogenesis, CXCR4/CXCL12 in prostate cancer, and CXCR7/CXCL12 in human hepatocellular carcinoma cells (20). Here, CXCL12 is linked to hepatocellular carcinoma.