CXCR4 is a receptor that is found on the surface of many different cell types in the body. It plays a role in immune system signaling between cells.

In cancer, evidence that CXCR4 is involved in the growth of tumors and their spreading throughout the body (metastasis) has been growing in recent years. For example, researchers have shown in studies in mice that blocking the action of CXCR4 inhibits metastasis. But its precise role in determining outcome and metastatic tendency, especially in lung cancer, is incompletely investigated.