Cell lineage heterogeneity in blast crisis of chronic myeloid leukaemia

Summary Blast cells from 45 patients with chronic myeloid leukaemia in blast crisis (CML‐BC) were immunologically phenotyped with a panel of 26 monoclonal antibodies and studied for terminal deoxynucleotidyl transferase (TdT) content. Out of 45 blast‐populations, 28 showed a myeloid, 14 a lymphoid, two a mixed and one an unclassifiable marker profile. In contrast to acute myeloid leukaemia (AML), we found frequent involvement of the thrombopoietic and erythropoietic systems in myeloid CML‐BC. Furthermore, the marker profile on blast cells in myeloid CML‐BC was different from that seen in AML. The blast cells in lymphoid blast crises of CML displayed the same lymphoid marker profile as those in acute lymphoblastic leukaemia. In three of 16 patients who were serially tested, we observed phenotypic changes in the blast cell populations. In one patient the blasts changed from lymphoid to myeloid type while remaining TdT‐positive; in another case the blasts switched from granulomonocytic TdT‐negative to granulomonocytic TdT‐positive. In the third patient erythroid precursor cells appeared as the disease progressed. The results indicate the capacity of blast populations in CML‐patients during blast crisis to differentiate along several pathways.