An immunoconjugate consisting of an anti-CD19 monoclonal antibody conjugated to the auristatin derivative monomethyl auristatin F (MMAF), with potential antineoplastic activity. Upon administration of denintuzumab mafodotin, the antibody moiety targets the cell surface antigen CD19, found on a number of B-cell-derived cancers. Upon antibody/antigen binding and internalization, the immunoconjugate releases MMAF, which binds to tubulin and inhibits its polymerization. Inhibition of tubulin polymerization may result in G2/M phase arrest and tumor cell apoptosis. This causes inhibition of cell growth of CD19-expressing tumor cells. CD19, a B-cell antigen, is overexpressed by a variety of different cancer cell types.