A substance being studied in the treatment of some types of cancer. It is made by linking the monoclonal antibody huC242 to a toxic substance called maytansinoid DM4. The monoclonal antibody binds to the surfaces of cancer cells and the maytansinoid DM4 enters the cells and blocks their growth. It is a type of immunotoxin. Also called maytansinoid DM4-conjugated humanized monoclonal antibody huC242.