Early T-precursor acute lymphoblastic leukemia with mature plasmacytoid dendritic cell proliferation

A 44-year-old man without a significant relevant medical history was admitted to our department for asthenia without other clinical signs. Blood count revealed leukopenia (2.7 × 10⁹/L), anemia (7.9 g/dL), and thrombocytopenia (75 × 10⁹/L) with 7% blasts. Bone marrow aspiration showed hypercellular marrow infiltrated by 92% blasts composed of 2 populations (panels A-C, May-Grünwald-Giemsa stain, original magnification ×1000): 60% immature blasts of medium size with an nuclear/cytoplasmic (N/C) ratio close to 1, and immature chromatin with prominent nucleoli (panel B); and 40% mature plasmacytoid dendritic cells of medium size with an N/C ratio close to 0.8 and fine chromatin with a cytoplasmic extension containing a few vacuoles (panel C). Flow cytometry revealed a blastic population positive for CD34, CD38, cCD3, CD7, CD13, CD33, and terminal deoxynucleotidyltransferase (TdT), and negative for CD117, CD1a, CD5, sCD3, CD4/8, myeloperoxidase, and HLA-DR. An expanded mature plasmacytoid dendritic cell population was positive for CD38, HLA-DR, CD33, CD4, CD11b, CD123, CD2, and CD304, and negative for CD34, CD56, TdT, cCD3, and CD13 (panels D-K). In conclusion, the patient showed early T-precursor acute lymphoblastic leukemia (ETP-ALL) with proliferation of plasmacytoid dendritic cells (pDCs). Karyotype showed trisomy 10 and targeted high-throughput sequencing revealed IDH2, DNMT3A, CXCR4, IKZF1, and NRAS mutations. No RUNX1 or TP53 mutation was observed.

This case highlights the possibility of pDC proliferation in ETP-ALL, not only in chronic myelomonocytic leukemia or acute myeloid leukemia. Further investigations of clonality association between ETP-ALL and pDCs would be of interest.

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