Aberrant phenotypes and quantitative antigen expression in different subtypes of canine lymphoma by flow cytometry

Flow cytometry may be a useful tool to analyze lymphoma samples that are obtained from fine needle aspirations (FNA). This study aimed to determine if flow cytometric analysis add more objective and standardized information on the cellularity and morphology of lymphoma cells to conventional cytology. The typical immunophenotype of different lymphoma subtypes was assessed and leukocyte marker expression was evaluated to determine which antigens were more frequently over- or under-expressed in these lymphoma subtypes. Fifty FNA lymph node samples were evaluated from canine lymphomas. Thirty-one samples were identified to be of B-cell origin, sixteen were identified to be of T/NK-cell origin and three cases were classified as acute lymphoblastic leukaemia with lymph nodes involvement. The most common B-cell lymphoma subtypes were centroblastic lymphomas, whereas three cases were atypical and classified as B-large cell pleomorphic lymphomas. Among the T/NK lymphomas, small clear cells, large and small pleomorphic mixed cells, large granular lymphocytic cells and small pleomorphic cells were identified. Aberrant phenotypes and/or antigen under/over regulation was identified in thirty out of forty-seven lymphoma cases (64%; 18/31 B-cell = 58% and 12/16 T-cell = 75%). In B-cell lymphomas the most frequent finding was the diminished expression of CD79a (45%). CD34 expression was also observed in four cases (13%). Among T-cell lymphomas the prevalent unusual phenotype was the under-expression or absence of CD45 (25%). These findings reveal flow cytometry may be useful in confirming the diagnosis of lymphoma, as the technique allows one to add useful information about morphology of the neoplastic cells and identify antigenic markers and aberrant phenotypes.