Pretreatment with an unlabeled anti-CD3 antibody blocked the targeting of the labeled antibody to the spleen, and pretreatment with both unlabeled CD3 and MUC16 antibodies blocked the targeting to both the spleen and the MUC16 + tumor, indicating that most of the targeting to the tumor is driven by the anti-MUC16 arm of the bsAb. The gene discussed is MUC16; the disease is neoplasm.