Therefore, prior to conducting pretargeting experiments using 68Ga and THPMe-NCS-huA33, PET imaging of the same tumour model was undertaken with directly labelled 89Zr-DFO-NCS-huA33 immunoconjugate, to verify that the xenografts expressed the A33 antigen targeted by the huA33 antibody and that 24 h was sufficient time for the radioimmunoconjugate to localise at the tumour site and clear from circulation. The gene discussed is GPA33; the disease is neoplasm.