Clinical pathological and epidemiological assessment of morphologically and immunologically confirmed canine leukaemia

Abstract

Traditionally, classification of leukaemia in dogs has relied on morphological examination and cytochemical staining patterns, but aberrant cellular morphology and stain uptake often curtails accurate categorization, and historical data based on this classification may be unreliable. Immunophenotyping is now the gold standard for classification of leukaemias. The purpose of this prospective study was to assess the clinical pathological and epidemiological features of a population of dogs with morphologically and immunologically confirmed leukaemia and to compare them within categories: acute and chronic lymphoid leukaemia (ALL and CLL), and acute and chronic myeloid leukaemia (AML and CML). There were 64 cases of morphologically and immunologically confirmed leukaemia: 25 cases of ALL, 17 cases of CLL and 22 cases of AML. Prevalence of B and T immunophenotypes in ALL and CLL was not statistically different. Dogs with AML were significantly younger than those with ALL at presentation (P = 0.04). Golden Retriever dogs in the study population were overrepresented in comparison with a control population of dogs (6/25 ALL cases, 8/64 leukaemia cases). No sex was overrepresented. Dogs with ALL had significantly more severe neutropenia (P = 0.001) and thrombocytopenia (P = 0.002) than those with CLL and had significantly more cytopenias. The severity and numbers of cytopenias seen in ALL and AML were not significantly different. Twenty-one of the leukaemia cases showed one cytopenia, fourteen had two cytopenias and twenty-one cases had pancytopenia. Anaemia was the most common cytopenia seen in isolation (17/21). No dogs had neutropenia without anaemia and/or thrombocytopenia. Total white blood cell counts were not different between the groups. The atypical cell counts within the peripheral blood were significantly higher in ALL than AML; both in isolation and as a percentage of the total white blood cell count (P = 0.03). This study strengthens the hypothesis that acute leukaemias give rise to more profound cytopenias, affecting more cell lines, than chronic leukaemias.