We report the case of a 31 year-old man diagnosed with an atypical acute leukemia difficult to characterize cytologically. The immunophenotyping identified a blastic population co-expressing myeloid, lymphoid B and lymphoid T markers suggesting the diagnosis of either a mixed phenotype acute leukemia (MPAL) or an early T-cell precursor acute lymphoblastic leukemia (ETP-ALL). Because of the poor prognosis linked to these leukemias, the patient benefited from chemotherapy targeting both myeloid and lymphoid components, followed by allogeneic hematopoietic stem cell transplantation. DNA-based techniques analyzing B and T-cell clonality identified partial rearrangements in immunoglobulin and TCR genes, allowing the monitoring of minimal residual disease. This observation highlights the difficulty to classify some atypical cases of acute leukemias. It emphasizes on the complementarity of cytomorphology, immunophenotyping by flow cytometry and molecular techniques in order to promptly characterize and treat these leukemias.
Keywords: acute lymphoblastic T-cell leukemia; cytology; flow cytometry; immunophenotyping; lymphoid clonality; mixed phenotype acute leukemia.