Canine lymphoproliferative disease characterized by lymphocytosis: immunophenotypic markers of prognosis.

BACKGROUND Canine lymphoproliferative disease often presents with lymphocytosis and is immunophenotypically diverse. HYPOTHESIS Immunophenotype predicts prognosis in canine lymphoproliferative disorders involving circulating lymphocytosis. ANIMALS Dogs that had peripheral blood evaluation performed by flow cytometry by the Clinical Immunology Service at Colorado State University between 2003 and 2005. METHODS Outcome data regarding treatment and survival were sought on patients with lymphocytosis comprising a single lymphocyte subset. Ninety-six patients that met the inclusion criteria had sufficient follow-up information to be included in the study. RESULTS Four main phenotypic classifications were found: CD8+ T-cell, CD21+ B-cell, CD4-8-5+ (aberrant T-cell phenotype), and CD34+ (undifferentiated progenitor). Expression of CD34 predicted poor outcome with median survival of 16 days (P < .0001) compared with other phenotypes. Within the CD8+ phenotype, dogs presenting with a lymphocytosis >30,000 lymphocytes/muL had significantly shorter median survival (131 days) than those presenting with <30,000 lymphocytes/muL (1098 days, P < .0008). Within the T-cell leukemias, there was no difference in outcome between dogs with CD4-8-5+ leukemia and dogs with the CD8+ T-cell phenotype nor was the loss of expression of the pan-leukocyte marker CD45 associated with decreased survival time. A CD21+ lymphocytosis composed of large cells was associated with shorter survival time (129 days) than those with smaller circulating cells (median survival not reached, P < .01). CONCLUSIONS AND CLINICAL IMPORTANCE Immunophenotyping provides an objective method for determining prognosis in lymphoproliferative disorders characterized by lymphocytosis.