Cytohistological and immunological classification of canine malignant lymphomas: comparison with human non-Hodgkin's lymphomas.

Non-Hodgkin's lymphomas (NHLs) in man are on the increase. They are also common in dogs, which, as close companions of man, may constitute a useful experimental model. However, comparisons cannot be made without a reliable morphological and immunological classification of canine NHL. Canine NHLs (n = 134) were classified on the basis of fine-needle lymph-node aspirates according to the Kiel classification, and 92 were re-classified according to the Working Formulation and the updated Kiel classification, in a histological and immunological study. The immunophenotype was determined (1) in 92 cases by the use of the pan-T anti-CD3 polyclonal antibody and the pan-B anti-mb1 monoclonal antibody on paraffin wax-embedded tissue sections, and (2) in 47 cases by the use of a panel of polyclonal and monoclonal antibodies on fresh preparations and frozen tissue. Cytological analysis showed a predominance of high-grade lymphomas (73.9%) over low-grade lymphomas (26.1%); it also demonstrated forms not reported in other species (small-cell variants, lymphomas with macronucleolated medium-sized cells [MMCs], and polymorphic lymphomas with a centroblastic component). Histological examination revealed the rarity of follicular lymphomas (2.2% of cases), an appearance suggestive of T-cell neoplasia (8.7% of cases), and evidence that some MMC lymphomas originated in the marginal perifollicular zones. Some (26%) of the lymphomas were of the T-cell phenotype: the majority of these consisted of small-cell, low-grade lymphomas and mycosis fungoides, the rest being either high-grade pleomorphic lymphomas (mixed or large-cell) or, rarely, high-grade, small noncleaved-cell, plasmacytoid lymphomas. No lymphoma expressed a double (T and B) phenotype. This study revealed similarities with, but also notable differences from, human NHL. In particular, the MMC lymphomas may constitute an interesting equivalent of human marginal zone B-cell lymphomas.