Canine T-cell Lymphomas: A Morphological, Immunological, and Clinical Study of 46 New Cases

TLDR

The aim of this study is to report 46 new cases of canine T‑cell lymphomas among a series of 140 lymphomas studied by immunophenotyping (incidence 32.8%). The study classified 46 canine T‑cell lymphomas into 13 low‑grade (small clear‑cell, pleomorphic small‑cell, and mycosis fungoides) and 33 high‑grade (pleomorphic mixed, large, lymphoblastic, and plasmacytoid) tumors, all CD3+ CD79a− with varied CD4/CD8 expression, and found common clinical signs such as generalized or regional lymphadenopathy, hepatosplenomegaly, extranodal disease, mediastinal masses, leukemia, and hypercalcemia, especially in lymphoblastic cases.

Abstract

The aim of this study is to report 46 new cases of canine T-cell lymphomas among a series of 140 lymphomas studied by immunophenotyping (incidence 32.8%). According to the updated Kiel classification adapted to the canine species, 13 were classified as low-grade and 33 as high-grade lymphomas. Among the low-grade lymphomas, five were small clear-cell lymphomas, three were pleomorphic small-cell lymphomas, and five mycosis fungoides. Among the high-grade cases, there were 11 pleomorphic mixed-, small-, and large-cell lymphomas, 6 pleomorphic large-cell lymphomas, 11 lymphoblastic lymphomas, and 5 unclassifiable high-grade plasmacytoid lymphomas. The cytohistologic features were highly suggestive of a T-cell phenotype on the basis of cell morphology (irregular nuclei and clear cytoplasms) (30/46 cases), a T-cell zone pattern, and the presence of hyperplastic postcapillary venules (22/46 cases). All 46 cases were CD3+ CD79a-, and among 34 cases investigated for CD4 and CD8 expression, 13 were CD4+CD8-, 13 were CD8+CD4-, and 8 were CD4CD8 double positive or double negative. The pleomorphic mixed lymphomas were mainly CD4+CD8- (6/7) and the lymphoblastic lymphomas were double positive or double negative (6/8). The main clinical, hematologic, and biochemical features were generalized (28/46) or regional lymphadenopathy (16/46), hepatosplenomegaly (15/46), extranodal involvement (11/46), mediastinal mass (9/46), and leukemia (8/46), which were mainly present in cases of lymphoblastic lymphomas and hypercalcemia (16/46).