Table 2 Classification of myelocytic leukemia, main characteristics and cases reported in horses
From: A review of current knowledge of myeloproliferative disorders in the horse
Type of myeloid leukemia | Main characteristics and identification | Equine cases reported in literature | |
AUL | Acute undifferentiated leukemia | Considered a separate entity of AML-M0. Even up to 100% of the total nucleated cells can be blasts in bone marrow or blood. Highly immature atypic cells. In humans, some AUL are classified as ‘unclassifiable’ leukemia | Not reported |
Acute myeloid leukemias | |||
AML-M0 | Acute myeloid leukemia | Blast cells ≥ 90% of myeloid cells. < 5% of blast cells in general circulation are stained with myeloperoxidase. No Auer blast cells. Ultrastructural detection of lysosomes with myeloperoxidase or immunophenotyping required for characterization | Not reported |
AML-M1 | Acute myeloblastic leukemia (without maturation) | > 90% of the non-erythroid cells are myeloblasts. Blasts with less than 10% cytoplasmic granulation. At least 5% of the population of blasts stained with Sudan Black B and myeloperoxidase. Auer rods may be present | Not reported |
AML-M2 | Acute myeloblastic leukemia (with maturation) | 30–90% of the non-erythroid cells are myeloblasts. At least 10% of the neoplastic cells shows maturation. At least 50% stained with myeloperoxidase and may have Auer rods | Clark et al. [17] |
AML-M3 | Promyelocytic | Predominance of promyelocytes in blood and bone marrow. Associated with recurrent genetic abnormalities in humans | Not reported |
AML-M4 | Myelomonocytic | Both granulocyte and monocyte differentiation. > 20% blast cells in blood or bone marrow. > 20% of bone marrow cells must be of monocyte lineage | Bienzle et al. [19] Blue et al. [20] Boudreaux et al. [21] Brumbaugh et al. [22] Buechner-Maxwell et al. [23] Mori et al. [24] Ringger et al. [25] Spiers et al. [26] Miglio et al. [12] |
AML-M5 | Monocytic | Peripheral monocytosis. Neoplastic monocytes comprise more than 80% of non-erythroid cells in bone marrow. Two subtypes: AML-5A: predominantly monoblasts (> 80%) AML-5B: mixture of monoblasts and promonocytes (< 80% blasts) | Burhardt et al. [27] Monteith and Cole [28] Latimer and White [29] |
AML-M6 | Acute erythroid leukemia Subtype M6A | Dual lineage with a co-production of myeloblasts and erythroblasts. > 50% of the total nucleated cells in bone marrow are of erythroid lineage; at least 30% myeloblast precursors | Not reported |
AML-M6 | Acute erythroid leukemia Subtype M6B | Undifferentiated or pronormoblastic immature cells the erythroid lineage > 80%. M: E ratio < 0.02:1 | Forbes et al. [32] Panziera et al. [32] |
AML M7 | Megakaryocytic | Blast cells > 20% of the circulating cells or bone marrow and at least 30% of the marrow cells is of megakaryocyte lineage | Not reported |
AML-M8 | Acute basophilic leukemia | Stain with toluidine blue. Metachromatic granules typical of mast cells or basophils | Furness et al. [37] |
Myeloproliferative neoplasms | |||
CGL | Chronic granulocytic leukemia | Proliferation of cell lineages of relatively mature neutrophils, eosinophils or basophils Relatively mature granulocytes predominate in blood marrow | Searcy and Orr [38] Johansson et al. [39] |
CEL | Chronic eosinophilic leukemia | Proliferation of eosinophil precursors with high number of eosinophils in blood, bone marrow or peripheral tissues. Immature or atypical eosinophils | Morris et al. [42] |
CBL | Chronic basophilic leukemia | Increased number of basophils in bone marrow and blood. Blast cells accounted for 17% of all nucleated cells. Positive staining to omega-exonuclease, naphtol AS-D chloroacetate esterase and Sudan Black B | Not reported |
Polycythemia vera or primary erythrocytosis | It affects all bone marrow cell lines and manifest itself with erythrocytosis. Sometimes accompanied by thrombocytosis and leukocytosis. Erythropoietin values within normal limits | Steiger and Feiger [49] McFarlane et al. [48] | |
ET | Essential thrombocythemia | Overproduction of megakaryocytes in bone marrow | Not reported |
CMoL | Chronic monocytic leukemia | Excessive proliferation of granulocytic and monocytic cells | Spiers et al. [26] |
CMMoL | Chronic myelomonocytic leukemia | Circulating myeloid blast cells can represent 5–10% of the leukocytes. Hypersegmented granulocytes and monocytes | Not reported |
Myelodysplasic síndromes | |||
MDS | Myelodysplastic syndrome | Ineffective hematopoiesis with dysplastic alterations affecting one to multiple cell lineages Hypercellular marrow, blasts count < 20%, concurrent peripheral cytopenia. AML can be developed after MDS | Durando et al. [10] Miglio et al. [12] |