Acute leukemias of ambiguous lineage

Example of the usefulness for lineage assignment of the combination myeloperoxidase (MPO), cCD13, cCD3, and cCD79a on a permeabilized sample of normal whole bone marrow (A–K) and a leukemic sample (L). Color code: red, polymorphonuclears; green, monocytes; purple, lymphocytes; cyan, immature cells defined as “not polymorphonuclears, not monocytes, not lymphocytes,” called the “bermudes” area by the GTLLF.²⁷ (A) Whole populations on a side scatter/CD45 “cartography” scattergram. (B) Whole populations on an MPO/cCD13 scattergram. (C) Whole populations on an MPO/cCD3 scattergram. (D) Whole populations on an MPO/cCD13 scattergram. (E) Polymorphonuclear gating of the MPO/cCD13 scattergram showing MPO gradient of expression. (F) Monocyte gating of the MPO/cCD13 scattergram showing weak MPPO labeling. (G) Lymphocyte gating of the MPO/cCD3 scattergram showing MPO-negative cCD3-positive T cells. (H) Lymphocyte gating of the MPO/cCD79a scattergram showing MPO-negative cCD79a-positive B cells. (I) Bermudes gating of the MPO/cCD79a scattergram showing hematogones. (J) Gating of the hematogones population in dark blue. (K) Backgating of the hematogones defined in J on the initial “cartography” scattergram. The same strategy would be used to identify the blastic population in a leukemic sample as shown in L for MPO positivity backgating. Mixed phenotype acute leukemia would show the coexpression of markers of different lineages such as cCD79 and MPO or cCD3 and MPO.

Example of a case of T/myeloid mixed phenotype acute leukemia. The 4 top scattergrams show the same combinations as in Figure 1. There is large population of blasts in the “bermudes” area, very few neutrophils, almost no monocytes, and a normal amount of lymphocytes. The latter mostly express CD79a. The blastic population coexpresses myeloperoxidase (with a spreading pattern) and cyt.CD3 as highlighted in the backgating illustrated in the middle panels. In another tube, these cells are shown to coexpress CD34 and faintly CD13 (bottom scattergram).

Example of mixed phenotype acute leukemia, not otherwise specified, T/myeloid diagnosed in immunochemistry. The material studied was a mediastinal biopsy from a young male patient. It was received formalin fixed. Immunostainings showed a diffuse infiltration of blasts with strong positivity for CD7, variable expression of CD3, weak positivity for CD33, and a fraction of blasts positive for myeloperoxidase. The blast population was also positive for TdT, CD2, and CD5 (weaker than normal T cells), as well as partly for CD117 and CD123 (not shown). There was some positivity for CD79a, which may be seen in some T lineage acute lymphoblastic leukemia. CD34, PAX-5, CD10, CD4, CD8, and CD1a were negative. A similar immunophenotype was found in a bone marrow biopsy that was diffusely infiltrated by blasts. There was no peripheral blood involvement. Cytogenetic studies showed a hyperdiploid karyotype.