Technology evaluation: CEA-Scan, Immunomedics Inc

Imaging of cancer by radioimmunoscintigraphy (RIS) following administration of radiolabeled monoclonal antibodies (mAbs) or fragments has been under development for two decades. Efficacy is a function of many variables: antigen expression on tumor cells relative to normal tissues and body fluids, affinity, specificity, pharmacokinetics and immunogenicity of the mAb and properties of the radionuclide and imaging techniques. CEA-Scan (a 99mTclabeled Fab' fragment of a mouse mAb directed against CEA) has several advantageous properties, and has been approved for use in colorectal cancer SPECT imaging in North America and Europe, and is also under investigation in Japan. It has been shown to complement CT in detecting recurrent or metastatic disease, even in the liver where 111In mAbs frequently fail. In breast cancer, it provides clearer identification of malignant disease in patients with indiscriminate mammography. Recently, it has also been used intra-operatively in radio-immunoguided surgery in both colorectal and breast cancer patients. These new applications are currently under active investigation and clinical trials are planned. Clinically useful information is obtained in a relatively high percentage of patients, which can alter treatment decisions. In most cases the benefits are in reducing unnecessary surgery or biopsies in inoperable patients, but major benefits (especially in colorectal cancer) would be obtained if new therapies effective against the RIS-detected minimal residual disease were forthcoming.