Patient Consent Statement
Written informed consent was obtained from the patient to publish this
report.
Keywords : Acute myelomonocytic leukemia, Acute lymphoblastic
leukemia, Flow cytometry, Myeloperoxidase, Alpha-naphthyl butyrate
esterase
Funding and Acknowledgement Statements : none
A 70-year-old man with an unremarkable past medical history presented to
our hospital because of fever and shortness of breath for two weeks. On
laboratory examination, he was found to have hyperleukocytosis with
abundant blasts in the peripheral blood (PB). (white cell count
103.47\(\times\)109/L (94.8% blasts), hemoglobin
level 65 g/L, platelet count 60\(\times\)109/L). Bone
marrow (BM) aspiration and trephine biopsy revealed a leukemic marrow
filled with small-sized blasts having scant cytoplasm without noticeable
cytoplasmic granules (Figure 1A), morphologically suggestive of acute
lymphoblastic leukemia. However, cytochemical stain for myeloperoxidase
(Figure 1B) and alpha-naphthyl butyrate esterase (Figure 1C) turned out
to be both positive. Additionally, flow cytometry of the BM (Figure 1D)
demonstrated that the blasts actually expressed cytoplasmic (cy) MPO,
CD117 (partial), CD33, CD11b, CD64, CD38, but lacked the expression of
cyCD3, cyCD79a, surface membrane (sm) CD3, CD19, CD34, HLA-DR, CD13,
CD14, CD35, CD300e. Aberrant expression of CD56 on these blasts was also
noted. Based on the results of lineage-specific stains and flow
cytometric analysis, the patient was diagnosed with acute myeloid
leukemia with myelomonocytic differentiation (French-American-British
(FAB) M4). Low-dose cytarabine and venetoclax was started for induction,
and he later achieved partial remission. We would like to raise the
recognition that acute myelomonocytic leukemia may present with blasts
resembling lymphoblasts based on morphological examination. A
multi-modality diagnostic procedure is necessary for making the correct
diagnosis and guiding appropriate treatment.
Figure legend:
(A) Bone marrow aspiration showed a leukemic marrow filled with blasts
having scant cytoplasm, and no cytoplasmic granules. (Liu’s stain, 1000X
magnification) The blasts stained positive for myeloperoxidase (B, 100X,
brown denotes positivity) and alpha-naphthyl butyrate esterase (C,
1000X, red denotes positivity). (D) Flow cytometric analysis of the
blasts; the majority of the blasts are colored red, with the
CD117-positive portion colored green.