A substance being studied in the imaging of breast cancer and some other types of cancer. It is made by attaching a radioactive substance called indium 111 to the monoclonal antibody trastuzumab (Herceptin). Trastuzumab binds to the human growth factor receptor 2 (HER2/neu) on some breast cancer cells and on several other types of cancer cells. Indium In 111 CHX-A DTPA trastuzumab is a type of radioimmunoconjugate.