A recombinant immunotoxin consisting of single-chain variable domain fragment antibody directed against the tumor-specific antigen EGFRvIII (MR1scFv) fused to domains II and III of the Pseudomonas exotoxin (PE38KDEL), with potential antineoplastic activity. Upon administration, the antibody moiety of anti-EGFRvIII immunotoxin MR1-1 binds to EGFRvIII; upon internalization, the exotoxin portion inhibits protein synthesis, resulting in a reduction in tumor cell proliferation of EGFRvIII- expressing tumor cells. EGFRvIII, a type III in-frame deletion mutation of the epidermal growth factor receptor (EGFR) gene, is expressed by a variety of cancers, including glioblastoma multiforme, non-small lung carcinoma, and breast carcinoma. Compared to intact IgG antibodies, single-chain antibodies such as MR1scFv are smaller and may penetrate tumors better. Pseudomonas exotoxin PE38KDEL was modified to remove the natural cell binding domain. Check foractive clinical trials using this agent.