Submitting Author: Tandon, Bevan, MD
Institution: Division of Hematopathology, University of Pittsburgh School of Medicine
Additional authors:Miroslav Djokic, M.D.
Session: AML with recurrent genetic abnormalities Part I

The patient is a one year old female with unremarkable past medical history presenting with marked peripheral blood leukocytosis including many blasts, anemia, and thrombocytopenia.

At the time of initial bone marrow biopsy, CBC data revealed the following:

Patient Value 6 months – 2 years

Normal Range

WBC 390.0 x10E+9/L [H] ( 6.0 – 17.5)

RBC 1.92 x10E+12/L [L] ( 3.70 – 5.30)

Hgb 8.0 g/dl [L] ( 10.5 – 13.5)

Hct 24.0 % [L] ( 33.0 – 39.0)

MCV 79.6 fL ( 70.0 – 86.0)

MCH 41.6 pg [H] ( 27.0 – 33.0)

MCHC 33.3 gm/dL ( 31.0 – 35.0)

RDW unavailable ( 11.5 – 15.0)

PLT 44 x10E+9/L [L] ( 150 – 450)

Peripheral Blood 6 months – 2 years

Differential ABS. No. Normal Range

POLYS 0.3 % (1.17) ( 1.00 – 8.50)

BANDS 0.7 % (2.73) [H] ( 0.00 – 1.00)

LYMPHS 8.7 % (33.93) ( 4.00 –13.50)

MONOS 2.0 % (7.80) [H] ( 0.05 – 0.70)

BLASTS 88.3% (344.37)

Review of the peripheral blood smear demonstrated numerous circulating blasts (Image 1) showing intermediate and large size, ample, lightly basophilic cytoplasm, sometimes prominent nuclear folding, dispersed chromatin, and variably prominent nucleoli. The bone marrow was essentially 100% cellular with predominant composition by blasts arranged in sheets (93% based on a manual aspirate differential cell count) (Image 2); mature monocytes comprised only a minority of cells present (3.7%). Within the marrow aspirate smears, the blasts appeared similar to that seen in the peripheral blood and some of the blasts displayed prominent cytoplasmic pseudopodial extensions (Images 3, 4). The background marrow cellularity showed reduced trilineage hematopoiesis.

Bone marrow aspirate flow cytometric studies revealed an aberrant blast population comprising approximately 70% of total cellular events and exhibiting the following phenotype:

CD45 positive (dim), CD34 negative, CD117 negative, HLA-DR positive, TdT negative, CD4 positive, CD56 positive, CD123 positive, CD11b positive, CD14 negative, CD64 positive, myeloperoxidase negative, CD15 positive, CD13 positive, CD33 positive, CD58 positive, CD19 negative, cytoplasmic CD3 negative, and negative for the other B and T lymphoid associated antigens assayed. (Images 5, 6)

Cytochemical stains were performed to further delineate the blast cellular origin and demonstrated positive staining with nonspecific esterase (alpha napthyl acetate esterase positive, chloroacetate esterase negative) (Image 7); alpha napthyl acetate esterase staining was inhibited by fluoride. The blasts additionally demonstrated butyrate esterase positivity (Image 8), also susceptibile to fluoride inhibition. Peroxidase stained occasional myeloid series elements, and the blasts were negative. (Image 9)

46,XX,t(9;11)(p22;q23)

Classical cytogenetic analysis demonstrated an abnormal female karyotype with a translocation involving the short arm of one chromosome 9 and the long arm of one chromosome 11. (Image 10)

nuc ish(MLLx2)(5’MLL sep 3’MLLx1)[204/209]

nuc ish(BCR,ABL1)x2

nuc ish(PML,RARA)x2

Fluorescence in situ hybridization (FISH) was positive for MLL gene rearrangement in 204 of the 209 interphase cells examined (97.6%). (Image 11).

FISH was negative for BCR/ABL1 and PML/RARA gene rearrangements.

Not performed.

The leukemic blasts show expression of CD4, CD56, CD123, CD13, CD33, and CD64. Coexpression of CD4, CD56, and CD123 strongly raises the possibility of involvement by blastic plasmacytoid dendritic cell neoplasm (BPDCN), which has been reported to rarely occur in pediatric populations (Jegalian et al. (2010) Haematologica: 95(11): 1873-1879), and which may show morphologic and immunophenotypic overlap with myelomonocytic cells (Cronin et al. (2012) AJCP: 137: 367-376). According to 2008 WHO blue book guidelines, demonstration of myeloid or lymphoid lineage excludes a diagnosis of BPDCN. However, in the absence of lineage specific marker expression (myeloperoxidase, CD3, or CD19), the minimal criteria required to establish myeloid or lymphoid differentiation based on antigen profiling and effectively exclude plasmacytoid dendritic cellular origin are not explicitly stated. Resolution of the differential diagnosis in this case was based on the results of cytochemical staining and cytogenetic studies. Cytochemical positivity for alpha napthyl acetate and butyrate esterases with susceptibility to inhibition by fluoride confirmed the monocytic origin of the leukemic cells. This was further supported by the presence of an MLL gene rearrangement with t(9;11)(p22;q23), demonstrated by classical and cytogenetic FISH studies.

The patient was initially managed with chemotherapy including cytarabine, daunorubicin, and etoposide, and leukophoresis was performed due to the extremely high white blood cell count. Unfortunately, the patient died shortly after initial diagnosis due to neutropenic sepsis complicated by cardiopulmonary collapse and multiorgan failure.

Acute myeloid leukemia with t(9;11)(p22;q23); MLLT3-MLL.

Acute myeloid leukemia with t(9;11)(p22;q23); MLLT3-MLL (AF9-MLL)

Case 384