Erythrophagocytosis by blasts in a case of de novo acute monoblastic leukemia with rare but characteristic t(8;16).

Erythrophagocytosis by leukemic blasts is a rare phenomenon. We report a case of a female diagnosed with acute monoblastic leukemia with leukemic blasts that were CD34 and CD117 negative, showing erythrophagocytosis, vacoulations, and a rare t(8;16) on bone marrow karyotype which is associated with a poor prognosis despite intensive chemotherapy. Meticulous bone marrow examination in such a scenario may point towards the presence of t(8;16) and help clinicians take a well-informed clinical decision.

Introduction

Advances in cytogenetic and molecular genetics are constantly being incorporated into the understanding of hematological neoplasms and now form a basis of the World Health Organization (WHO) classification of tumors of hematopoietic and lymphoid tumors as they form a distinct diagnostic, prognostic, and therapeutic categories.[1] We herein report a case of erythrophagocytosis by leukemic blasts in acute monoblastic leukemia which on karyotyping showed the presence of t(8;16) which is associated with a poor prognosis and may in future find a place in the WHO classification.

Case Report

A 31-year-old female presented with a history of high-grade fever and melena. On systemic examination, she had enlarged bilateral cervical lymph nodes without any organomegaly. An initial blood examination revealed hemoglobin of 7.1 g% with a high total leukocyte count of 97.8 × 109/L and thrombocytopenia with a platelet count of 36 × 109/L. There were 78% blasts in the peripheral blood. Her bone marrow examination revealed 80% blasts which were three to four times the size of a mature lymphocyte with open chromatin, two to three prominent nucleoli, and grayish blue cytoplasm with many cells showing the presence of cytoplasmic vacuoles. Few cells showed the presence of erythrophagocytosis [Figure 1]. Flow cytometric immunophenotyping (Beckman Coulter Navios [USA] and analyzed using Kaluza software version 1.2) performed on the bone marrow aspirate (BMA) sample showed the gated cells in the blast region to be moderate positive for CD45, CD33, CD64, CD36, and CD56; dim expression of CD38 and HLA-DR; dim partial expression of CD14, CD15, and myeloperoxidase. These cells were negative for CD34 and CD117 along with other markers of T-cell and B-cell lineage. Two 17 h unstimulated overnight BMA cultures with and without colcemid were setup using RPMI 1640 with 20% fetal bovine serum for conventional cytogenetics. Analysis of 20 metaphases using Ikaros software (MetaSystems GmbH, Altlussheim, Germany), revealed the presence of neoplastic clone characterized by a balanced translocation between the short arms of chromosomes 8 and 16 in all the 20 metaphases and the karyotype was reported as 46, XX, t(8;16)(p11;p13)(20) as per the ISCN 2013 [Figure 2]. Final diagnosis rendered as per the WHO 2008 classification was acute myeloid leukemia, NOS-AML-M5a with t(8;16). Due to financial constraints, the patient decided for supportive management and died within 33 days of diagnosis.

Figure 1

Erythrophagocytosis by a monoblast showing an engulfed red blood cell (arrow mark, Leishman stain, and × 100 oil immersion)

Figure 2

Karyogram showing t(8;16) reported as per ISCN 2013 as 46, XX, t(8;16)(p11;p13)(20) (abnormal chromosomes 8 and 16 placed in the right side of their homolog chromosomes and marked with arrows, GTG staining and banding method × 100 oil immersion, processed using IKAROS software)

Discussion

The t(8;16) is a rare cytogenetic event that has been reported in just over 100 cases till date in both de novo and treatment-related acute myeloid leukemia with a median age of 59.4 years, a female predominance, and AML M4, M5 phenotype.[2] While extramedullary involvement, skin infiltration, lymphadenopathy, and disseminated intravascular coagulation are important clinical presentations, the presence of erythrophagocytosis by leukemic blasts with or without cytoplasmic vacuoles is a crucial cytological finding.[23] This translocation leads to a fusion of KAT6A (or MYST3 or MOZ) gene located on 8p11 with CREBBP (CBP) on 16p13, both of which belong to the family of histone acetyltransferases with characteristics of transcriptional coregulators. The aberrant histone acetylation as a result of inhibition of RUNX1-mediated transcription is believed to mediate leukemogenesis in this disease entity.[456] Camós et al. in their study of three cases of t(8;16) using gene expression profiling (GEP) found upregulation of genes such as PRL, C20orf103, RET, GGA2, ICSBP1, ITGA7, DAP, IRAK1, and PPARG while STAT5A and STAT5B were significantly underexpressed.[7] The GEP also showed an upregulation of homeobox genes HOXA9 and HOXA10, their cofactor MEIS1, and upregulation of AKR7A2, PBX3, NICAL, and IRAK1B genes all of which are also upregulated in acute leukemia with rearranged MLL gene.[789]

The t(8;16) occurs as a sole abnormality as in the present case in ~53.3% of cases. Most common secondary cytogenetic abnormality associated with t(8;16) is trisomy of chromosome 8.[3] In t-AMLs, it may occur with abnormalities of chromosome 7 or as a part of complex karyotype.[2] The entity needs to be differentiated from “myeloid and lymphoid neoplasms with FGFR1 abnormalities” due to similar breakpoints, i.e., 8p11. Although neoplasms with FGFR1 abnormality may be present at any age, their median age of presentation is 32 years with a male predominance, eosinophilia, absence of erythrophagocytosis by leukemic blasts, presence of FGFR1 rearrangement, and no specific predilection to any FAB classification.[10]

Erythrophagocytosis is an uncommon phenomenon with hematological malignancies reported in <1% of the cases and when present it is characterized by phagocytosis by benign histiocytes.[11] Literature regarding erythrophagocytosis by leukemic blasts is extremely rare and is seen predominantly with monoblastic and monocytic leukemias.[12] Rare case reports of erythrophagocytosis by blasts have been described in biphenotypic leukemia, AML with t (16;21)/TLS/FUS-ERG fusion, AML M0, and B lymphoblastic leukemia, both with deletion 20q, AML M0 with t(9;22), and B lymphoblastic leukemia with t(12;21).[1112131415] The mechanism of phagocytosis by leukemic blasts is unknown.[11] Phagocytosis, in general, is the process that leads to ingestion of the particle by a cell and involves binding through receptors for complement CR1 (binding C3b) and CR3, receptors for IgG-Fc receptors, and receptor for fimbriae-gp 150 which is followed by ingestion.[11] Although none of these receptors have been reported on myeloblasts, some researchers have reported the presence of Fc receptors in lymphoblasts.[16] The fact that phagocytosis by leukemic blasts is uncommon in lymphoblasts than in myeloblasts a more complex mechanism is postulated rather than mere presence of Fc receptors.[11]

Immunophenotypically, these leukemias are CD34 and CD117 negative with a characteristic immune profile corresponding to AML.[3]. Similar to the acute leukemia with rearranged MLL gene, acute leukemia with t(8;16)/KAT6A–CREBBP fusion is also associated with a poor prognosis though Coenen et al. in their study of 62 pediatric cases of AML with t(8;16) found no difference in the outcome as compared to other AMLs.[2479]

Accurate identification of t(8;16) by bone marrow cytogenetic studies is mandated due to aggressive nature and poor prognosis associated with this entity. The presence of erythrophagocytosis in BMA smears, with or without vacoulations, in a case of monoblastic leukemia should prompt a search for t(8;16), that would assist a well-informed clinical decision.

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Conflicts of interest

There are no conflicts of interest.