An antibody-drug conjugate (ADC) composed of the trastuzumab biobetter HM2 conjugated, in a site-specific manner, to monomethyl auristatin E (MMAE), an auristatin derivative and potent microtubule disrupting agent, with potential antineoplastic activity. Upon administration of ALT-P7, the antibody moiety targets and binds to human epidermal growth factor receptor 2 (HER2) on tumor cells. Upon antibody/antigen binding and internalization, the MMAE moiety is released, binds to tubulin and inhibits its polymerization, which results in G2/M phase arrest and apoptosis. HER2 is a receptor tyrosine kinase (RTK) that is overexpressed by many cancer cell types.