This monograph explains the considerable impact that monoclonal antibodies and molecular probes have had on the diagnosis of tumor types and sub-types. It explains how radiolabelled monoclonal antibodies have also been used as imaging agents to try to improve the oncologist's ability to define residual tumor deposits after combination chemo/radiotherapy. Finally, the childhood malignancies that still have a poor prognosis are presented, and new novel ways of therapy are explained.