Single‐cell multiplex immunocytochemistry in cell block preparations of metastatic breast cancer confirms sensitivity of GATA‐binding protein 3 over gross cystic disease fluid protein 15 and mammaglobin

For a single marker, GATA3 displayed the highest sensitivity. The addition of MMG for hormone receptor-positive breast cancers and GCDFP15 for hormone receptor-negative breast cancers further increased sensitivity. The low proportion of multimarker-positive cells suggested that the coexpression observed with traditional ICC is attributable to intratumoral heterogeneity, not genuine coexpression.