A fully human monoclonal antibody (MoAb) against human A1 domain of tenascin-C, in small immunoprotein (SIP) format conjugated with iodine 131 with potential antineoplastic activity. Iodine I 131 MoAb F16SIP binds to tenascin-C on the vascular tissues and delivers cytotoxic radiation to the tumors, thereby minimizing systemic radiotoxicity. Tenascin-C is a glycoprotein of the extracellular matrix, and the large isoform of this matrix protein is expressed and restricted around vascular structures in the tumor stroma of a variety of different tumors.