B-lymphoblastic leukemia with Burkitt-like morphology and aberrant myeloperoxidase expression: A diagnostic conundrum

[摘要] A 48-year-old woman was diagnosed with B-acute lymphoblasticleukemia (B-ALL) in 1996 and was treated with chemotherapy andan allogeneic sex mismatched unrelated donor stem cell transplant(SCT) in 1997 at another institution. She presented to our hospital in January 2020 with pancytopenia. Bone marrow (BM) biopsy(Figure 1) showed hypercellular (95%) BM with sheet of blasts (A,hematoxylin and eosin, 10×). Aspirate smears showed 80% blaststhat were large with dispersed chromatin, inconspicuous nucleoli, andbasophilic cytoplasm with numerous vacuoles reminiscent of Burkittlike morphology (B, Wright and Giemsa, 50×). Flow cytometry (FC)immunophenotyping showed B-lymphoblasts positive for CD19, CD20(subset), CD22, CD34, CD38 (decreased), CD79a, HLA-DR, and TdT (Cand D) with an aberrant myeloperoxidase (MPO) expression (E) thatwas dimmer in blasts (red) compared with background granulocytes(gray). Blasts were negative for myeloid and/or monocytic markersincluding CD11c, CD13, CD14, CD33, CD64, CD117, and lysozyme.Immunohistochemistry highlighted blasts positive for Pax5 (F, 20×) andMPO with a granular cytoplasmic staining pattern (G, 20×). Cytochemistry showed 35% of blasts positive for MPO (H, 500×) and negativefor butyrate esterase.

[关键词] B-lymphoblastic leukemia;Burkitt-like;flow cytometry;immunohistochemistry;myeloperoxidase