An antibody-drug conjugate (ADC) composed of a monoclonal antibody directed against a specific myeloma antigen and conjugated to monomethyl auristatin E (MMAE), an auristatin derivative and a potent microtubule inhibitor, with potential antineoplastic activity. Upon administration, the monoclonal antibody moiety of DFRF4539A selectively binds to a specific protein expressed on the surface of myeloma cells. Upon internalization and proteolytic cleavage, MMAE binds to tubulin and inhibits its polymerization, which results in G2/M phase arrest and tumor cell apoptosis.