Antibody fragment

The CEA-Scan antibody fragment was developed as a replacement for first-generation antibody imaging agents based on intact murine antibodies. Intact murine antibodies stimulate high anti-mouse antigen (HAMA) levels, concentrating in the liver and clearing slowly, thus unable to reliably detect liver metasteses. By comparison, the Fab' antibody fragment in CEA-Scan clears rapidly from the blood and liver via renal excretion. Because it's so small — weighing less than 50,000 Daltons — and because it lacks the antibody-stimulating Fc "tail" — arcitumomab is virtually nonimmunogenic.

To make a nuclear image of the colorectal tumors and metastases where arcitumomab binds, this antibody fragment is labeled with technetium-99m, the most commonly used nuclear medicine isotope.