The cytology, histology and prevalence of cell types in canine lymphoma classified according to the National Cancer Institute Working Formulation.

No significance has been shown yet between the cytological subtypes of canine lymphoma and clinical behaviour. This paper describes and illustrates the cytological and histological criteria for application of the National Cancer Institute Working Formulation classification system, a scheme with demonstrated prognostic capability for human non-Hodgkin's lymphomas, to a series of 285 canine lymphomas. The Working Formulation can be used without difficulty for canine lymphomas. Low grade follicular tumors were found to be much less common, and high grade, aggressive tumors much more common than these cell types in humans. Low grade tumors tend to have low mitotic rates and high grade tumors tend to have high mitotic rates. There may be an association between hypercalcemia and lymphoblastic cell type. A review of available literature data for canine lymphomas suggests that prognostic extrapolation of clinical behaviour based on human lymphoma data may be possible. These results suggest that there may be strong similarities of morphology and behaviour between human non-Hodgkin's lymphomas and canine lymphomas.