Submitting Author: McMahon, Christine, MD
Institution: Montefiore/Albert Einstein College of Medicine
Additional authors:K.H. Ramesh, PhD, Linda Cannizzaro, PhD
Session: Acute leukemias of ambiguous lineage

A fourteen-year old girl presented with a 2 month history of lymphadenopathy, tonsillar hypertrophy, and increasing shortness of breath. Imaging studies showed a mediastinal mass and splenomegaly. CBC showed a moderate granulocytosis, with normal erythroid, platelet, lymphocyte, and eosinophil counts.

1. Lymph node, cervical, formalin-fixed.

Lymph node architecture is extensively effaced by two distinct abnormal cell populations. In the cortical regions, there are medium-sized lymphoid cells with round nuclei, moderately fine chromatin, and scant cytoplasm (“blue area”). In the hilar region, there are numerous granulocytes in various stages of immaturity (promyelocytes, myelocytes, metamyelocytes, bands), interspersed with small, mature lymphocytes.

2. Bone marrow, iliac crest, formalin-fixed, acid decalcified.

Hypercelllur marrow infiltrated by blasts with interspersed myeloid elements showing markedly left-shifted granulocytic maturation.

1. LYMPH NODE

Flow Cytometry: 53% abnormal T Lymphoblasts

Positive markers: CD45 (dim) CD3 (cytoplasmic, but not surface),CD2, CD5 (weak), CD7, CD13, CD19 (weak).

Negative markers: CD3 (surface), CD4, CD8, T-cell receptors (alpha-beta and gamma-delta).TIA1, CD16, CD56, cTdT, CD57, CD123, CD34, CD117, CD33, myeloperoxidase, HLA-DR, cCD22, kappa, lambda

Immunohistochemistry:

Lymphoid cells (blue area on H&E):

Positive Markers: CD45, CD3, CD2, CD7, weak CD5 (weak), CD79a (weak, partial), and CD99.

Negative Markers: CD1a, CD4, CD8, CD34, CD117, CD123, CD33, TdT, CD10, CD20, PAX5, TIA1, granzyme B, CD30, CD15, EMA, CD25, ALK1, CD68, myeloperoxidase.

Myeloid cells (pink area on H&E):

Positive Markers: CD33, CD15, CD68 (KP1), myeloperoxidase.

Negative Markers: CD34, CD117.

2. BONE MARROW

Flow cytometry:

Population A: Predominantly lymphoid blasts with low side scatter (36%)

Positive markers: CD2, CD7, cytoplasmic CD3, weak CD19, weak CD79a, CD13, CD33 (dim), CD45 (dim)

Negative markers: surface CD3, CD4, CD5, CD8, CD1a, CD9, CD10, CD20,

CD22, cytoplasic CD22, IgM, kappa, lambda, HLA-DR, CD11b, CD11c, CD14,

CD64, CD56, CD91, CD123, CD163, TDT, CD34, CD117, myeloperoxidase (minimal staining compared to control).

Population B: Immature myeloid cells with intermediate side scatter (37%)

Positive markers: CD33 (strong), CD4, myeloperoxidase, CD64, HLA-DR,

CD11b (partial), CD11C (partial), CD2, CD7, CD13, CD19 (partial), CD45 (dim)

Negative markers: cytoplasmic CD3.

Immunohistochemistry:

Approximately 30-40% diffusely scattered blasts interspersed

Positive markers: CD2, CD3, CD7

3. PERIPHERAL BLOOD (slides not available)

Flow Cytometry:

15% abnormal cells that express cytoplasmic (but not surface) CD3,CD2, CD7, CD19, cytoplasmic CD79a, CD13, myeloperoxidase (weak), and CD45 (weak), but not CD34, CD117, CD1A, CD4, CD5, CD8, CD10, CD11b, CD33, CD56, cytoplasmic CD22, cytoplasmic IgM, kappa, or lambda.

1. Lymph node: FISH studies performed on bone marrow cells and/or touch preprations of the lymph node show no evidence of a BCR-ABL fusion gene or translocations involving the MLL or FGRR1 loci.

2. Bone marrow aspirate: complex karyotype. 46,X,t(X;9)(q13;p24),del(3)(q12),t(4;12)(q12;p13),t(11;14)(p13;q11.2),

del(13)(q13q31),del(16)(q22),del(18)(q21)[16]/46,XX[4].

FISH: Homozygous deletion of CDKN2A(9p21) in 92% of 200 cells; Loss of 3'ETV6 (12p13) in 87.5% of cells; Loss of 3'TCR (14q11.2) in 90% of cells studies. No evidence of a BCR-ABL fusion gene or rearrangements involving the MLL, FGRR1, or IGH loci.

The translocation t(4;12)(q12;p13) has been associated with undifferentiated acute myeloid leukemia (FAB M0)or acute leukemia of ambiguous lineage, suggesting that it affects an early progenitor cell that can differentiate along multiple pathways.

This is an unusual case of an immature hematopoietic neoplasm is difficult to classify that comprises at least two distinct cell populations and expresses markers from three different lineages. The dominant component seen in the lymph node and initial bone marrow biopsy most closely resembles a T lymphoblastic lymphoma/leukemia with aberrant (weak) expression of the B-cell markers CD19 and CD79a and the myeloid marker CD33. In addition to the dominant lymphoid component, there is a population of variably immature myeloid cells found in the hilar portions of the lymph node, the bone marrow, and the peripheral blood. The myeloid component most closely resembles a myelodysplastic/myeloproliferative neoplasm and co-expresses myeloperoxidase with both T-cell and B-cell markers, but does not express the blast markers such as CD34 and CD117. In the peripheral blood, expression of myeloperoxidase, cytoplasmic CD3, CD19, and cytoplasmic CD79a was detected on the same cells.

Follow up:

The patient was initially treated with T lymphoblastic leukemia-type chemotherapy, with improvement of the lymphadenopathy. Increasing leukocytosis prompted a repeat bone marrow biopsy, which showed immature cells with a myeloid/T/B immunophenotype. She was then treated with AML-type chemotherapy and had a significant response, however the cytogenetically abnormal cell population remained detectable. Six months after the initial diagnosis, she relapsed with CNS, blood, and bone marrow involvement.

Hematopoietic neoplasm of ambiguous lineage (bilineal, triphenotypic) with complex cytogenetic abnormalities including t(4;12)(q12;p13).

Additional immunostaining performed by the conference consensus group on lymph node sections:

MPO: Positive in blasts

Mixed phenotype acute leukemia, NOS

Case 356