Case 78

Submitting Author: Boyd, Jonathan Dale, MD
Institution: Brody School of Medicine at East Carolina University
Additional authors:Gregory A. Gagnon, MD and Ridas Juskevicius, MD
Session: AML with recurrent genetic abnormalities Part I

HISTORY

The patient is a male in his forties with history of alcohol abuse and upper GI bleed presented with a three month history of weight loss, fevers, chills and nights sweats. His blood smears were found to contain numerous blasts prompting transfer to our institution for hematologic work up. He was found to have WBC 20.6 k/uL (composed of 2.1k/uL neutrophil, 0.4k/uL lymphocyte, 1.9k/uL monocyte, 0.4k/uL band and 15.9k/uL blasts). He was also thrombocytopenic (126 k/uL) and anemic with hemoglobin of 9.0 g/dL, MCV of 111 fL, RDW 13.1%. He was started on tretinoin after peripheral blood examination and was continued on this therapy until cytogenetics results prompted transition to idarubicin and cytarabine. Complete response was seen to standard AML chemotherapy (7+3) but not tretinoin with decrease in blast count and hypocellular/ acellular marrow at day 14 and marrow regeneration with normal trilineage hematopoiesis on day 40.

DETAILS

Formalin fixed, paraffin-embedded, H&E stained marrow biopsy section and air-dried, Diff-Quik stained touch preparations from the left iliac spine demonstrated a hypercellular marrow containing a diffuse infiltrate of blasts (75%) with only few more mature myeloid cells and rare admixed megakaryocytes. The blasts were intermediate to large in size, with irregular, frequently folded nuclei, immature chromatin, prominent nucleoli, and moderate amount of pale basophilic cytoplasm containing occasional abnormal granules and single thick Auer rods. Some more differentiated myeloid precursors and PMN's were dysplastic with nuclear hypo-lobation. Erythropoiesis was hypoplastic, but normoblastic and without dysplasia or ringed sideroblast formation.

IMMUNOHISTOCHEMISTRY AND FLOW CYTOMETRY

Flow cytometry of peripheral blood showed a large population of events with moderate CD45 staining and low side scatter, corresponding to blasts (approximately 65%). The blast cells had an immature abnormal myeloid immunophenotype (CD34+, CD117+, CD33+, CD38+, HLA-DR+, MPO+, CD13+) with no significant expression of any specific lymphoid markers. A small proportion of blasts also express CD56.

CYTOGENETIC FINDINGS

45,X,-Y,t(2;21;8)(p23;q22;q22),del(9)(q12q22)

Cytogenetic analysis of GTG banded metaphases has revealed an abnormal clone in all cells examined. The clone is characterized by a translocation between chromosomes 2, 8 and 21. An additional deletion of 9q and loss of the Y chromosome were also part of the clonal changes.

MOLECULAR FINDINGS

The fluorescence in situ hybridization (FISH) study on the sample received was positive for the RUNX1T1−RUNX1 gene fusion. Unique sequence double fusion DNA probes targeting the RUNX1T1 (8q22) and RUNX1 (21q22) gene regions (Abbott Molecular Inc.) showed one RUNX1T1−RUNX1 gene fusion signal, two RUNX1T1 (ETO) signals and two RUNX1 (AML1) signals in 136 of 150 interphase cells analyzed. This pattern suggests a three−way translocation involving RUNX1T1 and RUNX1. Fluorescence in situ hybridization (FISH), using unique sequence DNA probes for the PML and RARA gene region (Vysis, Inc.) was normal. The FISH analysis showed the normal two PML and two RARA hybridization signals without fusion in all 200 interphase cells analyzed.

INTERESTING FEATURES

This case contains the novel complex variant non reciprocal translocation t(2;21;8)(p23;q22;q22) with fusion of RUNX1T1/RUNX1 (ETO/AML1) confirmed by FISH. Additionally, this case contained del(9q) and loss of sex chromosome (-Y), secondary chromosomal abnormalities frequently associated with AML with t(8;21). The clinical significance of this unusual cytogenetic variant translocation is not clear. Our case showed some morphologic differences from the typical classic AML with t(8;21). Marrow blast proportion was very high, there were no significant morphologic features of myeloid maturation and blasts showed frequently folded or bilobed nuclei and short, thick Auer rods initially leading to concern for possible acute promyelocytic leukemia (APL).
Despite this variant morphology and cytogenetic features, our patient showed excellent response to standard AML therapy, similar to typical AML with t(8;21). The only previously reported cases of AML with t(2;8;21) had different breakpoints of chromosome 2 (p12) and were associated with an AML-M4Eo morphology. Other variant three way translocations resulting in RUNX1T1/RUNX1 fusion have been reported with some of these cases showing poor response to therapy, unlike typical AML with core binding factor abnormalities. Our case illustrates that variant translocations although resulting in a typical RUNX1T1/RUNX1 fusion, may lead to somewhat altered morphology which, in turn, can complicate initial morphologic diagnosis. The clinical significance of these genetic variants remains unclear and further studies involving more patients are needed.

PROPOSED DIAGNOSIS

AML with (variant) translocation t(8;21)(q22;q22)(RUNX1T1/RUNX1)

CONSENSUS DIAGNOSIS

Acute myeloid leukemia with (variant) t(8;21)(q22;q22); RUNX1T1-RUNX1