Moreover, we observed these SPIO+ human macrophages were distributed throughout tumours with very few signs of cell clumping in the tumour vasculature following MRT as seen by labelling sequential sections of tumours using an antibody against human CD68 (a pan macrophage marker) and a histological stain for iron (Prussian blue) (Fig. 2c). The gene discussed is CD68; the disease is neoplasm.