Lorvotuzumab (also known as huN901) is a humanized monoclonal antibody that targets CD56 (neural cell adhesion molecule, NCAM), a cell-surface glycoprotein expressed on a subset of normal neuroendocrine cells and natural killer (NK) cells. It is most widely studied as the antibody component of an antibody-drug conjugate (ADC) called lorvotuzumab mertansine (IMGN901). In this ADC, the antibody is conjugated to the potent maytansinoid cytotoxic agent DM1 via a disulfide linker. Upon binding to CD56-positive tumor cells, the ADC is internalized, and DM1 is released intracellularly to disrupt microtubule assembly, leading to cell death. It has been clinically evaluated primarily for the treatment of CD56-positive malignancies, such as small cell lung cancer (SCLC), multiple myeloma, and ovarian cancer.