Metadherin, a protein that controls metastasis, and variants of metadherin are described. DNA sequences encoding the same and methods of production are described. Therapies involving the application of metadherin, binding agents that bind to metadherin, such as antibodies, and expression modulating agents, such as siRNA, are described. The use of metadherin or metadherin variants for delivering desired substances to particular lung tissue is described. A method of diagnosing metastatic cells based on the presence of metadherin is described.