Biodistribution and tumour localisation of 131I SWA11 recognising the cluster w4 antigen in patients with small cell lung cancer.

The biodistribution of radiolabelled SWA11, a mouse monoclonal antibody recognising the cluster w4 group antigen associated with small cell lung cancer (SCLC) was studied in patients with SCLC. Five patients were injected intravenously with approximately 5 mCi of 131I conjugated to 1 mg of SWA11. The half-life of the radiolabel in blood was short but there was a prolonged second phase of clearance with a half-life of about 40 h. Tumour was detected by gamma camera imaging two patients. However, most of the whole body radioactivity was located in the bone marrow. At least 35% of the radioactivity in blood 18 h after injection was bound to circulating granulocytes and this probably accounted for the unusual biodistribution of the radiolabel in man. This study shows that the biodistribution of radiolabelled SWA11 in man differs from human tumour xenograft models and that the antibody in unsuitable for targeting therapy to SCLC in man.