A radioimmunoconjugate containing the recombinant humanized monoclonal antibody trastuzumab conjugated with the bifunctional, macrocyclic chelating agent tetra-azacyclododecanetetra-acetic acid (DOTA) and labeled with the radioisotope copper Cu 64 with radioisotopic activity and potential use as an imaging agent. The trastuzumab moiety of copper Cu 64-DOTA-trastuzumab binds with high affinity to the extracellular domain of human epidermal growth factor receptor 2 (HER2). Upon binding, the radioisotope moiety may be detected using positron emission tomography (PET), thereby allowing the imaging and quantification of HER2-expressing tumor cells. HER2, a tyrosine kinase and client protein of heat shock protein 90 (Hsp90), may be overexpressed on the cell surfaces of various tumor cell types. Check for active clinical trials using this agent. (NCI Thesaurus)