Submitting Author: Brown, Noah Aaron, MD
Institution: University of Michigan
Additional authors:Maria Pletneva MD, PhD; Megan Lim MD, PhD
Session: AML with recurrent genetic abnormalities Part I

A 70-year-old male with a history of coronary artery disease, diabetes, and hypertension presented with 4 days of dyspnea on exertion and fever reaching 101F. He was admitted with suspected atypical pneumonia. During his admission, the patient's respiratory status deteriorated requiring intubation and blood pressure support. He was noted to have progressive anemia, thrombocytosis and monocytosis prompting a bone marrow biopsy.

All specimens were formalin fixed. Bone marrow core biopsy specimen was initially fixed in acetic acid-zinc-formalin and briefly decalcified with formic acid-formalin. Aliquots of marrow were submitted in RPMI for cytogenetic and molecular studies.

The bone marrow core biopsy was hypercellular for age (50-60%) with markedly decreased erythroid and megakaryocytic elements with myeloid expansion. Bone marrow aspirate smear demonstrated 58% blasts and promonocytes as well as 16% eosinophils including numerous forms with large, prominent basophilic granules. Iron staining of the aspirate showed increased storage iron without ring sideroblasts. The peripheral blood smear revealed neutropenia, normocytic anemia, thrombocytopenia and monocytosis with circulating promonocytes and blasts (17%). A peripheral eosinophilia was not seen.

Flow cytometry performed on the marrow aspirate demonstrated approximately 16% myeloblasts expressing dim CD2, CD4, CD13, CD33, CD34, CD64 and CD117 with moderate CD11b and CD36. There was also an expansion of monocytic elements expressing variable CD11c and CD14 which may represent promonocytes.

Cytogenetic analysis demonstrated a normal male karyotype, 46,XY[20]. Additional studies were performed using fluorescence in situ hybridization given the concern for a CBFB-MYH11 fusion based on the morphologic features in the bone marrow biopsy and aspirate material. Dual fusion signals indicative of the typical inv(16) or t(16;16) were not observed using the Cytocell dual fusion probe set. However, 85.0% (170/200) of interphase cells examined had a fusion-positive, variant signal pattern (1R1G1F). Together with metaphase FISH analysis, these results indicate a molecular-level insertion of MYH11 into the CBFB locus at 16q22.

FISH also was performed to rule out a possible deletion of 12p using the TEL-AML1 probe set; these results were entirely normal.

Molecular analysis demonstrated the absence of FLT3 internal tandem duplication or D835 mutation based on capillary electrophoresis of multiplex PCR products subjected to restriction endonuclease digestion. There was no NPM1 insertion based on capillary electrophoresis following PCR amplification of exon 12. There was no CEBPA mutations based on bidirectional Sanger sequencing of 2 overlapping fragments of the CEBPA gene. The KIT D816V mutation was absent based on allele-specific PCR.

This case represents an acute myelomonocytic leukemia with morphologic features suggestive of CBFB-MYH11 including abnormal eosinophil precursors. However, conventional cytogenetics failed to demonstrate the typical inversion 16 or t(16;16). Instead there was a molecular level insertion of MYH11 into the CBFB locus which was only apparent by fluorescence in situ hybridization.

Acute myeloid leukemia with CBFB-MYH11

Acute myeloid leukemia with cryptic inv(16) or t(16;16) or t(16;16); CBFB-MYH11

Case 280