The present invention discloses monoclonal antibody 8H9 which binds to the 4Ig domain isoform of the human B7-homolog 3, 4Ig-B7H3. The present invention provides a method of improving the prognosis or prolonging the survival of a subject bearing tumor cells, the method comprises administering to the subject a composition comprising an effective amount of an agent capable of binding to an antigen recognized by monoclonal antibody 8H9.
