T lymphoid/myeloid bilineal crisis in chronic myelogenous leukemia

We describe 2 cases of 'bilineal' crisis in chronic myelogenous leukemia (CML) with T cell and myeloid phenotypes. In both cases, morphocytochemically distinct myeloid and T lymphoid blast populations proliferated simultaneously in the phase of blastic crisis-myeloperoxidase (MPO)-positive, CD7⁺/CD33⁺ myeloblasts in the peripheral blood, and MPO-negative, periodic acid Schiff (PAS)-positive lymphoblasts in the lymph nodes. In each case, common karyotypes containing Ph¹ translocation were demonstrated in both the peripheral blood and the lymph node samples. In Case 1, the lymph nodes were occupied by > 90% lymphoblasts, which were positive for CD2, cytoplasmic CD3 (cCD3), CD5 and CD7 and terminal deoxynucleotidyl transferase (TdT)I but negative for myeloid antigens. Myeloblasts and T lymphoblasts showed an identical rearrangement of the bcr gene by Southern blotting analysis, although the clonal rearrangement of the T cell receptor (TcR)-δ gene was seen only in T lymphoblasts. In Case 2, simultaneous proliferation of myeloblasts and lymphoblasts was documented morphocytochemically in the lymph node, and a flow cytometric analysis revealed the coexistence of CD7⁺CD33⁺ and CD7⁺/CD33^- blast populations. Each blast population was enriched by antibody-conjugated immunomagnetic beads; the former was positive for MPO by 64% but negative for cCD3 and TdT, whereas the latter was positive for cCD3 and TdT but negative for MPO (<1%). CD7⁺/CD33⁺ myeloblasts and CD7⁺/CD33^- lymphoblasts showed an identical rearrangement of the bcr gene. Neither TcR-β, TcR-γ nor the TcR-δ gene was clonally rearranged in either population. These observations clearly indicate that T lymphoid and myeloid blasts share common Ph¹-positive progenitors, and that Phi-positive T lymphoid/myeloid progenitors are probably involved in the development of blastic transformation in some percentage of CML patients.