B7-H3, a new member of the B7 family of immune-regulatory molecules, was identified in 2001 by database searches of a human dendritic cell-derived cDNA library. It is a type I transmembrane protein, which expresses in certain normal cells and tissues, such as dendritic cells, as well as the liver, lung, breast, placenta, and prostate. Aberrant expression of B7-H3 has been reported in a wide range of solid cancers, including brain, lung, pancreatic, colorectal, liver, and breast cancers, as well as in hematologic malignancies, such as acute leukemia and multiple myeloma, and it is associated with more advanced disease and poor prognosis.