A: IHC staining of myeloperoxidase to identify bone marrow-derived immature myeloid cells at the invasive front of human breast ductal adenocarcinomas (a & d). H&E staining of sequential tumor sections figure b to a, and e to d, respectively. Figure c and f are negative controls. Scale bar, 100 uM for all figures. B: Flow cytometry analysis of immature myeloid cells from single cell suspension of human breast ductal adenocarcinomas (stage 2–3). The analyzed cells were gated as 7AAD negative (top left panel, P1), negative for lineage markers including CD3 for T cell, CD19 for B cell, CD56 for NK cell, CD40/CD86/HLA-DR for dendritic cells, and CD14 for monocytes, and CD33, CD34 and CD15 positive (top right panel, P2). A histogram for FITC positive myeloid cells is shown in the lower right pane, with isotype control in the lower left panel.