IKAROS protein is reduced in BM blasts from CML patients with advanced-phase myeloid disease, but not from patients with BCR-ABL1–negative AML. Immunohistochemical staining for IKAROS protein (magenta) in representative BM trephine biopsy sections counterstained with hematoxylin from normal BM and patients with CML in CP, AP, and myeloid BC as indicated, as well as patients with BCR-ABL1–negative AML and BCR-ABL1⁺ (Ph⁺) B-ALL. AP-CML #1 shows loss of IKAROS staining in the primitive cells in the paratrabecular regions (black arrow) in contrast to strong IKAROS staining in the residual maturing CP-CML cells (yellow arrow). AP-CML #2 similarly shows loss of IKAROS in blasts (black arrows), but not in residual maturing cells (yellow arrows). The original magnification is shown on the bottom right of each panel.