Submitting Author: Mirza, M. Kamran, MD, PhD
Institution: University of Chicago
Additional authors:Gordana Raca MD PhD, Jennifer McNeer MD MS, and John Anastasi MD.
Session: AML with recurrent genetic abnormalities Part I

The patient is an 18-year-old male who presented to his primary care physician with a 1 week history of fatigue, headache and joint pain. He also had easy bruisability and chin numbness. His family had noted a significant weight loss (~20 lbs) over a 1 month period. An initial work-up at the referring institution revealed leukocytosis (WBC 16 K/uL) and thrombocytopenia (40 K/uL). Blasts were noted on the peripheral smear. The patient was sent to our institution for additional work-up. His physical examination was relatively unremarkable except for shoddy cervical and supraclavicular lymphadenopathy.

Peripheral blood smear and bone marrow biopsy

(Bone marrow, right posterior iliac crest, B5 and formalin fixation and decalcified)

Hematologic indices at the time of bone marrow biopsy were as follows: WBC 16 K/uL, Hb 12.4 g/dL, Hct 39.8%, MCV 96 fL, platelet count 60 K/uL.

The peripheral blood smear (figure 1) revealed a leukocytosis, normocytic anemia and thrombocytopenia. Blasts accounted for 7% of the leukocyte differential and were variable in size ranging from intermediate to very large cells (4-5 times the size small lymphocytes) with fine chromatin, prominent nucleoli, and occasional Auer rods, consistent with myeloblasts. Immature and maturing granulocytic elements (1% promyelocytes, 7% myelocytes, 1% metamyelocytes, 5% band forms and 19% segmented neutrophils) were also present and there were 5% monocytes. Some of the mature granulocytes and monocytes were very large, 2-4 times normal size. The erythrocytes were normochromic, normocytic with mild anisocytosis. Rare schistocytes, red blood cell fragments and polychromatophilic cells were noted. Platelets were markedly decreased in number, but of normal granularity.

The bone core biopsy (figure 2A) was 100% cellular and filled by sheets of large cells with abundant amphophilic cytoplasm, with indented/folded and irregular nuclear contours with single and multiple prominent nucleoli and blast-like chromatin. These blasts displayed what appeared to be monocytic/macrophage differentiation. Some blasts were very large with sizes up to 4-5 times that of small lymphocytes. Residual normal hematopoiesis was virtually absent. A reticulin stain confirmed the presence of reticulin fibrosis (grade 1-2+/3).

The bone marrow aspirate smear (figure 2B) revealed no spicules but scattered cells were present throughout. Blasts or immature cells accounted for almost 70% of the cells. Similar to the peripheral smear and bone core specimen, some blasts were quite large with abundant cytoplasm, fine chromatin and prominent nucleoli. Residual hematopoiesis was markedly reduced with significantly low numbers of granulocytic and erythroid precursors. Megakaryocytes were not appreciated. A combined esterase stain (figure 3) performed on the touch preparation revealed a major population (>50%) of cells with reactivity for alpha naphthyl butyrate (ANB) with a minor population highlighted by chloracetate esterase (CAE) and some dual positive cells.

Flow cytometry performed on a specimen of peripheral blood revealed blasts (accounting for 18-19% of all cellular events) with a phenotype of CD34+, HLA-DR+, cMPO+, partial CD117+, weak CD33+, CD13+ and no expression of B or T cell antigens.

Immunohistochemical stains were performed and interpreted with appropriately reactive controls. The blasts were immunoreactive for lysozyme and were negative for CD68 and S100.

Abnormal mosaic karyotype (figure 4)

45,X,-Y,t(8;21)(q22;q22)[2]/89,idemx2,-17[6]

(Note: only 8 metaphase cells were available for analysis)

No evidence of NPM1 mutation

No evidence of FLT3 ITD

No evidence of FLT3 D835 Variant

The case is of interest due to the tetraploid karyotype and double t(8;21)(q22;q22); RUNX1-RUNX1T1. A double t(8;21) can be seen with a tetraploid karyotype in about 1% of all cases of t(8;21) AML (1). Like the current case these tetraploid cases do not usually exhibit the morphologic or immunophenotypic findings typical of t(8;21) AML such as the “M2” morphology, the salmon-colored granulation, the Chediak-Higashi like granules and the common expression of CD19 or CD56 on the blasts. In our case there was a monocytic differentiation, as well as the large size of some blasts and differentiated cells corresponding to the tetraploid clone.

A fascinating correlate is that there are rare cases of precursor B ALL with tetraploidy and frequently these have t(12;21)(p13;q22) also involving RUNX1 i.e., ETV6-RUNX1. In one study 12 of 783 cases of precursor B-ALL had tetraploidy and 8 of 9 of these had ETV6-RUNX1 (2).

Interestingly, RUNX1 has also been implicated in the polyploidization of normal megakaryocytes through silencing of non-muscle myosin heavy chain IIB. It is believed that the reduced MYH10 prevents the contractile ring from forming preventing cell division and propelling the megakaryocytes to undergo polyploidization (3)

It is interesting to consider whether the tetraploid RUNX1 leukemias develop through a similar mechanism.

References:

1. Xiao Z, Liu S, Liu X, Yu M, Hao Y. Tetraploidy or near-tetraploidy clones with double 8;21 translocation: a non-random additional anomaly of acute myeloid leukemia with t(8;21)(q22;q22). Haematologica. 2005 Mar;90(3):413-4.

2. Attarbaschi A, Mann G, König M, Steiner M, Dworzak MN, Gadner H, Haas OA; Austrian Berlin-Frankfurt-Münster Cooperative Study Group. Near-tetraploidy in childhood B-cell precursor acute lymphoblastic leukemia is a highly specific feature of ETV6/RUNX1-positive leukemic cases. Genes Chromosomes Cancer. 2006 Jun;45(6):608-11.

3. Lordier L, Bluteau D, Jalil A, Legrand C, Pan J, Rameau P, Jouni D, Bluteau O, Mercher T, Leon C, Gachet C, Debili N, Vainchenker W, Raslova H, Chang Y. RUNX1-induced silencing of non-muscle myosin heavy chain IIB contributes to megakaryocyte polyploidization. Nat Commun. 2012 Mar 6;3:717.

Acute myeloid leukemia (AML) with double t(8;21)(q22;q22); RUNX1-RUNX1T1 associated with a near tetraploid karyotype and monocytic differentiation

Case 289