Submitting Author: Yared, Marwan Antoine, MD
Institution: University of Arkansas for Medical Sciences
Session: AML with recurrent genetic abnormalities Part I

This is a 69 year old female with history of hypertension who presented to her primary care physician complaining of fatigue, non-productive cough, and subjective fever for 3 weeks prior to presentation. Complete blood count showed a low white blood cell count. The patient was admitted to an outside hospital for fever and neutropenia. A bone marrow biopsy performed at the outside hospital showed invovlement by acute leukemia. The patient was transferred to our hospital for further management. On admission, a CBC showed a WBC count of 0.68 K/uL with 23.7% neutrophils, a hemoglobin level of 9.9 g/dL, and a platelet count of 136 K/uL. Bone marrow biopsy and aspirate were repeated for morphologic, phenotypic, cytogenetic, and molecular analysis.

The peripheral blood smear reflected the observed pancytopenia with only rare, morphologically unremarkable white blood cells present. Blasts, atypical promyelocytes, or Auer rods were not identified.

The left posterior iliac crest bone marrow aspirates and acid zinc formalin-fixed, paraffin-embedded sections of the bone marrow biopsy showed a hypercellular marrow for age (cellularity: 50%). The granulocytic cell series was hyperplastic and left-shifted with increased blasts comprising 22% of myeloid cells. The blasts were large-to medium sized, had scant cytoplam, open chromatin, and prominent nucleoli. Atypical promyelocytes and myelocytes showing nuclear bi-lobation or deep grooves were also present. Auer rods were not identified. The erythroid and megakaryocytic cell lines were slightly hypoplastic but morphologically unremarkable.

Flow cytometric analysis performed on the bone marrow aspirate showed a myeloid cell population with moderate side scatter and CD45 expression comprising 67% of total events. Two subpopulations were identified within this gate.

The first subpopulation comprised about 40% of the cells in the gate (27% of total events) and was positive for CD34, CD13, CD33, CD117, CD15, myeloperoxidase, and CD2, and negative for HLA-DR, CD3 (surface and cytoplasmic), CD4, CD5, CD7, CD8, CD10, CD14, CD19, CD20, CD56, and TdT.

The second subpopulation comprised about 60% of the cells in the gate (40% of total events) and was positive for CD13, CD33, CD117, CD15, CD56 (subset), myeloperoxidase, and CD2, and negative for CD34, HLA-DR, CD3 (surface and cytoplasmic), CD4, CD5, CD7, CD8, CD10, CD14, CD19, CD20, and TdT.

Conventional cytogenetic analysis performed on the bone marrow aspirate showed 46,XX,t(15;17)(q22;q11~12) in all 20 metaphases analyzed.

Interphase FISH was performed on the bone marrow aspirate with a dual color, dual fusion PML/RARA probe set (Abbott Molecular, Des Plaines, IL) used to detect the (15;17) translocation associated with APL. This test was scored on an automated image analysis platform. The technical results underwent a manual technologist review for quality control purposes.

A minimum of 200 interphase nuclei were scored and abnormal fusion signals were observed in 51% of nuclei examined, indicative of the presence of the PML/RARA fusion.

Given the observed pancytopenia at presentation, the expected bone marrow morphology for this case of acute promyelocytic leukemia would be that of the hypergranular variant with abundant atypical promyelocytes showing numerous Auer rods. Also, a significant increase in myeloblasts would not be expected, reflected by lack of expression of CD34 and HLA-DR. Instead this case shows a myeloblast population comprising 22% of myeloid cells and expressing CD34. Of note, the blasts also aberrantly express CD2. Atypical, more mature myeloid precursors including promyelocytes and myelocytes are also present, showing nuclear bi-lobation or deep grooves. Auer rods, however, were not identified.

This case highlights the importance of entertaining the diagnosis of APL and prompt communication of this suspicion to the clinician whenever any hints exist, no matter how sublte, that this could be the diagnosis. This should be done even if other features of the case (increased myeloblasts comprising more than 20% of myeloid cells; expression of CD34; lack of atypical promyelocytes with cytoplasmic Auer rods) do not support the diagnosis of APL. Finally, this case also highlights the importance of cytogenetic and molecular analyses to rule the diagnosis of APL in or out, in morphologically and phenotypically atypical cases.

Acute promyelocytic leukemia with t(15;17)

Acute promyelocytic leukemia with t(15;17)(q22;q11~12); PML-RARA

Case 106