The critical role of flow cytometry in diagnosing aberrant T-cell acute lymphoblastic leukemia in a dog: case report

Acute lymphoblastic leukemia (ALL) with double-negative T-cell phenotype (CD4-/CD8-) represents a rare presentation in dogs requiring flow cytometry for definitive diagnosis. An eight-year-old German Shepherd presented with progressive lethargy, weight loss, and severe cytopenias. Complete blood count (CBC) revealed severe leukocytosis (90,500/μL) with 99% atypical lymphocytes, non-regenerative anemia, and thrombocytopenia. While blood smear examination demonstrated lymphoblastic morphology, flow cytometry was essential to identify the aberrant immunophenotype CD3+/CD4-/CD8-/CD34+, confirming ALL with arrested differentiation at the earliest T-cell stage. Palliative chemotherapy produced minimal response, and the patient died 11 days post-diagnosis. Flow cytometry results were received 5 days post-mortem, highlighting challenges in turnaround time for specialized diagnostics. This case emphasizes that flow cytometry is essential for accurate diagnosis of acute leukemia with aberrant phenotypes and underscores the need for rapid immunophenotyping services to enable timely therapeutic intervention.