Photomicrograph shows staining patterns of tumor cells detected in peripheral blood. (A) Cell detected with the Bre-3 anti–MUC-1 antibody; (B) tumor cell detected with AE1/AE3 anti-cytokeratin cocktail. There is cell membrane staining in the anti–MUC-1 preparation and coarse granular or fibrillary cytoplasmic staining of tumor cells with anti-cytokeratin, consistent with the distribution of cytokeratin intermediate filaments.