Case 10

Submitting Author: Patel, Jay Laxmanbhai, MD
Institution: University of Calgary
Additional authors:Janette van den Berghe, Fariborz Rashid-Kolvear
Session: Acute leukemias of ambiguous lineage

HISTORY

The patient is a five year-old female who presented with fever and lymphadenopathy. She was found to be anemic and leukopenic on CBC (hemoglobin 97 g/L, hematocrit 29%, WBC 2.1x10^9/L, ANC 0.8x10^9/L). No blasts were seen on peripheral smear examination.

DETAILS

A bone marrow aspirate and biopsy (right iliac crest) was performed. The aspirate smears and touch preparations show a marked increase in blasts (~50%) which range in size from intermediate to large and show increased nuclear-cytoplasmic ratio, irregular nuclear contours and variably conspicuous nucleoli. There is a background of reduced trilineage hematopoiesis. Significant dyspoiesis is not appreciated. The core biopsy sections are hypercellular (90-100%) with sheets of atypical mononuclear cells consistent with blasts. There is a background of reduced trilineage hematopoiesis.

IMMUNOHISTOCHEMISTRY AND FLOW CYTOMETRY

Flow cytometry (performed on bone marrow aspirate): An atypical population of CD45 dim/negative, low side-scatter events was observed which represent blasts. The blasts express CD10, CD19, CD22, partial CD13, partial CD33, CD34, cCD79a, nTdT, HLA-Dr and dim/moderate MPO. MPO expression on blasts was confirmed by a Children's Oncology Group reference laboratory on a subsequent bone marrow specimen. CD3 (surface and cytoplasmic), CD15 and CD117 are negative.

Immunohistochemistry (performed on core biopsy): The blasts are positive for CD79a and PAX5. Only rare blasts, in addition to maturing myeloid cells, appear to stain positive for myeloperoxidase and lysozyme.

Cytochemical stains were also performed. A minor subset of cells present on aspirate smear stained positive for myeloperoxidase, but these were difficult to distinguish from left-shifted maturing myeloid elements. The majority of blasts are negative for myeloperoxidase and NSE by cytochemistry.

CYTOGENETIC FINDINGS

63-64<3n>,XXX,add(1)(p13),-2,-3,-7,+10,-13,-14,-15,-16,-19,-20,+21,+21[cp6]/

63-65<3n>,idem,?add(2)(p23),-10,+mar[cp2]/46,XX,[26]

FISH for t(9;22):NO TRANSLOCATION

FISH for MLL: NO REARRANGEMENT

FISH for t(12;21):NO TRANSLOCATION

FISH for 4: 23.5% ABNORMAL

FISH for 10: 25.5% ABNORMAL

Of the 34 mitoses that were analyzed, 26 are normal and 8 have a complex abnormal karyotype. Of the abnormal mitoses, two cytogenetically related clones are present. The stemline, observed in 6 mitoses, has a structural abnormality of the short arm of one copy of chromosome 1 and trisomies of several chromosomes including chromosome 4 in addition to tetrasomy 10 and pentasomy 21. A further sideline is present with each of the aforementioned abnormalities with the exception of trisomy 10 (instead of tetrasomy 10) and presence one unidentified marker chromosome and possible abnormality of the short arm of chromosome 2.

For each probe set, there is no evidence of t(9;22), t(12;21), or MLL rearrangement. However, three signals for ABL1, BCR, MLL, and ETV6 were observed in 11.5%, 11.5%, 17.5%, and 17.5% of nuclei respectively. FISH result also shows 4-5 signals for RUNX1 in 22.5% of nuclei examined.

Of the scoreable nuclei, an abnormal signal pattern with 3 signals for chromosomes 4 and 10 was observed in 23.5% and 17.8% of nuclei respectively.

Additionally, 8% of nuclei have four signals for chromosome 10.

This result is consistent with the presence of high hyperdiploidy and double trisomy 4 and 10.

MOLECULAR FINDINGS

None performed.

INTERESTING FEATURES

This was a difficult case from the diagnostic perspective due to the expression of myeloperoxidase by flow cytometry, which was unequivocal and independantly confirmed by a COG reference laboratory (Seattle, WA) on a separate sample. However, the remaining immunophenotype and genetic studies were typical of B lymphoblastic leukemia with hyperdiploidy. Aware that the distinction between mixed phenotype acute leukemia, B/myeloid and typical B lymphoblastic leukemia has clinical significance for this patient, do the flow cytometry findings confirm true myeloid differentiation as implied by the current WHO classification?

PROPOSED DIAGNOSIS

Mixed phenotype acute leukemia, B/myeloid, with hyperdiploidy

CONSENSUS DIAGNOSIS

Mixed phenotype acute leukemia, B/myeloid (with hyperdiploidy)