Submitting Author: Azzato, Elizabeth Mae, MD, PhD
Institution: Department of Pathology and Laboratory Medicine, Hospital of the University of Pennsylvania, Philadelphia, PA
Additional authors:Cooley Pantazis, Department of Pathology, Munroe Regional Medical Center, Ocala FL Adam Bagg, Department of Pathology and Laboratory Medicine, Hospital of the University of Pennsylvania, Philadelphia, PA
Session: AML with recurrent genetic abnormalities Part I

A 62-year-old male with multiple medical problems including dementia was noted to have pancytopenia, which prompted a bone marrow biopsy (November 2012). While this marrow is not currently available for review, it was reported (by both the primary pathologist and the extramural academic consultant) to be normal. However, cytogenetic analysis revealed the following:

47, XY, del(3)(p12p23),inv(16)(p13.1q22),+22[3]/46,XY[11]. Given this finding in the setting of a reportedly normal bone marrow biopsy, a repeat biopsy was requested to rule out acute leukemia or possible laboratory error. This second marrow, which is the one submitted to the workshop, was performed one month later, in December 2012, and was also interpreted to be normal, again by both the primary pathologist and the extramural academic consultant.

Biopsy site: Iliac crest

The biopsy was formalin-fixed and submitted after decalcification.

H&E stained sections show trabecular bone with cellular marrow that is normocellular for age with trilineage hematopoietic elements and an M:E ratio of approximately 1:1. There is not a histologically evident or obvious expansion of blasts or eosinophils, and maturation to segmented neutrophils is present. However, in some areas, myelopoiesis does appear left-shifted with focal collections of immature cells that do not appear to exceed 5-10% overall.

The Wright-Giemsa stained aspirate smear lacks cellular spicules and is hemodilute, with a paucity of bone marrow elements. However, rare blasts/promonocytes (~2%) are noted and only a single mature eosinophil with few basophilic granules is seen.

A tandem CBC showed a WBC 2.5 x 103/l, HGB 8.3 g/dL, PLT 78 x 103/l.

An automated differential count showed 53.8% neutrophils, 38.7% lymphocytes, 4.2% monocytes, 1.5% eosinophils, 1.2% basophils.

Unfortunately, no peripheral blood smear is available for review.

Flow cytometric analysis on the hemodilute bone marrow aspirate reportedly reveals no expansion of blasts.

Karyotype: 47,XY,add(3)(p21),inv(16)(p13q22),+22[3]/46,XY[14]

FISH: Low level positive result for CBFB gene rearrangement

Nuc ish(CBFBx2)(5’CBFB sep 3’CBFBx1)[7/500]

Not performed.

This case is notable for the confirmed cytogenetic finding of inv(16)(p13.1q22) in an otherwise mostly unremarkable bone marrow biopsy with a paucity of easily identifiable blasts/promonocytes. The involvement of CBFB was also confirmed by FISH with a breakapart probe, albeit in a lower percentage of cells (1.4% vs 18% by karyotype), which suggests a growth advantage in the cells with the abnormal karyotype. Adding legitimacy to the cytogenetic finding is the concurrent trisomy 22, a common additional finding in inv(16) AML. Furthermore, loss of part of 3p is also present, again in both analyses. This deletion is well documented in a spectrum of myeloid neoplasm, although not (to our knowledge) in inv(16) AML.

Although inv(16)(p13.1q22) should be considered an acute leukemia regardless of blast count, at least some increase in promonocytes/blasts and abnormal eosinophils is normally expected. While there are reported cases of inv(16) AML with a blast/promonocytes count under 20% , the counts usually approach 20%, and a search of the literature found no case reports of inv(16)(p13.1q22) AML with a blast/promonocyte count as low as seems to be apparent here. Of course the paucity of characteristic cells in this case may reflect the non-representative nature of the aspirate smear, and there is an impression of some focal immaturity on the biopsy; nevertheless, an abnormal clone (that meets some criteria for “complex cytogenetics”, given the presence of 3 aberrations) clearly emerged from the hemodilute aspirate despite rare morphologically apparent neoplastic cells. This begs the question, how low of a blast /promonocyte count can warrant a diagnosis of acute leukemia?

Unfortunately, our review of this case is hampered by the lack of a good quality representative bone marrow aspirate and a lack of IHC to interrogate the left-shifted myeloid cells in the bone marrow. However, despite these limitations, blasts/promonocytes do not seem to be overtly increased, and thus we felt this case warranted submission to the workshop.

(*) At the time of submission (1/31/13) unstained recuts on this consultation case had not yet been submitted to us and hence we were unable to (1) do IHCs or (2) send unstained recuts. We would be happy and willing to do so after the deadline, if the panel is interested in this case.

AML with inv(16)(p13.1q22) without overt morphological evidence of acute leukemia

Morphologically normal bone marrow biopsy with cytogenetic evidence of inv(16)(p13.1q22) in 3/17 metaphases and by FISH (CBFB rearrangement) in 7/500 cells

Recommend rebiopsy with adequate aspirate smear assessment and close clinical followup

Case 269