Case History

A 34-year-old man with pancytopenia, mediastinal mass and splenomegaly. Bone marrow flow cytometry showed an abnormal population with this phenotype: CD45lo, cytoplasmic CD3-, CD19-, CD10-, CD34+, CD13heterogeneous, CD33 heterogeneous, HLA-DR+, TdT+, MPO-. What is the diagnosis?

  1. Acute myeloid leukemia
  2. T-Acute lymphoblastic leukemia
  3. Acute undifferentiated leukemia
  4. Mixed phenotype acute leukemia

 Question Photo 1 Bone marrow flow cytometry Question Photo 2 Bone marrow biopsy   

Answer:  ā€œCā€ Acute undifferentiated leukemia


Acute undifferentiated leukemia is a very rare leukemia subtype that shows no lineage specific antigens. It cannot be assigned to either the lymphoid or myeloid lineage. By definition, they lack the T-cell and myeloid markers cCD3 and MPO and do not express B-cell markers such as cCD22, cCD79a or strong CD19. They also lack the specific features of cells of other lineages, such as megakaryocytes or plasmacytoid dendritic cells. Blasts often express HLA-DR, CD34, and/or CD38 and may be positive for TdT. The limited data suggest that these leukaemias have a very poor prognosis.

Source: Swerdlow, S. H. (Ed.). (2017). WHO classification of tumours of haematopoietic and lymphoid tissues. International Agency for Research on Cancer.

Case contributed by: Diana Morlote, MD., Hemepath Fellow, UAB Pathology