Keynote Message
Haemopoietic neoplasms are clonal disorders of haemopoietic cells and include myeloid and lymphoid leukaemia, lymphoma, and plasma cell tumours. Acute myeloid leukaemia (AML) is a neoplastic proliferation of early non-lymphoid haemopoietic precursors with minimal or absent maturation. The diagnosis rests on a marrow blast count exceeding 20% of all nucleated cells, although this is often much higher. The blast cells may be identifiable with light microscopy or may be poorly differentiated, in which case cell lineage is confirmed with flow cytometric immunophenotyping using myeloid-specific markers such as myeloperoxidase, MAC-387 and CD14, as well as CD34 (a marker of haemopoietic precursors). Acute lymphoid leukaemia (ALL) is characterised by the presence of lymphoblasts in the marrow and blood with cytopenias of one or more major cell lines and an absence of substantial lymphadenopathy. The cells have B or T cell immunophenotype and may express CD34 whilst MHCII expression is often absent. In acute undifferentiated leukaemia, the blast cells do not express any lineage-specific markers although do express CD45 and often CD34. The prognosis for acute leukaemia is poor with much shorter remission times than is seen with high-grade lymphoma.
Lymphoma is a heterogenous group of diseases with different prognoses, and it is increasingly recognised that lymphoma should be classified using a combination of morphology and immunophenotype, according to the WHO or updated Kiel classification scheme. Lymphoma can infiltrate the bone marrow and blood, but affected animals usually have marked lymphadenopathy, in contrast to the absent, mild or moderate lymphadenopathy seen in acute leukaemia. The lymphoid cells in various types of high-grade lymphoma (HGL) are often larger and have more prominent nucleoli than in ALL, although morphology alone often cannot distinguish ALL and HGL. A combination of clinical presentation, morphology, and flow cytometry is required. Case examples will be used to illustrate how a combination of morphology and immunophenotype is used to classify various haemopoietic neoplasms.
Key References
1. Bennet AL, Williams LE, et al. Canine acute leukaemia: 50 cases (1989–2014). Vet Comp Oncol. 2017;15:1101–1114. doi:10.1111/vco.12251.
2. Sayag D, Fournel-Fleury C, Ponce F. Prognostic significance of morphotypes in canine lymphomas: a systemic review of the literature. Vet Comp Oncol. 2017. doi:10:1111/vco.12320.
3. Martini V, Poggi A, Riondato F, Gelain ME, Aresu L, Comazzi S. Flow-cytometric detection of phenotypic aberrancies in canine small clear cell lymphoma. Vet Comp Oncol. 2015;13:281–287. doi:10.1111/vco.12043.
4. Villiers E, Baines S, Law A-M, Mallows V. Identification of acute myeloid leukemia in dogs using flow cytometry with myeloperoxidase, MAC387, and a canine neutrophil-specific antibody. Vet Clin Pathol. 2006;35:55–71. doi:10.1111/j.1939-165X.2006.tb00089.x.