Submitting Author: Sojitra, Payal, MD
Institution: Loyola University Medical Center
Additional authors:Timothy VandenBoom, Reshma Marri, Sucha Nand, Dong Chen, David S. Viswanatha and Girish Venkataraman
Session: Therapy-related myeloid neoplasms

A 61 year old Italian-American male with past medical history of diabetes and Stage T3N0 colon cancer (s/p hemicolectomy with adjuvant chemotherapy in 2003) presented in April 2011 with a complaints of a marked increase in fatigue, generalized weakness, dry cough, and dizziness for 3-4 weeks. The patient also admitted to a 25 pound weight loss over the past few months. Physical examination revealed mild jaundice as well as hepatosplenomegaly, confirmed by CT. Laboratory results revealed a new onset anemia and thrombocytopenia (WBC 4,000/microliter; Hemoglobin 7.2 g/dL; Platelet 109,000/microliter). A bone marrow biopsy was performed for further evaluation of the patient. A serum tryptase study showed markedly elevated serum tryptase levels (830 ng/mL). Over the next two weeks, the patient reported increasing symptomatic anemia requiring blood transfusions. By the end of the second week, the patient developed worsening respiratory distress, developed sepsis as well as multiorgan failure and died shortly thereafter.

The core biopsy was obtained from the left posterior iliac crest. The received specimen was fixed in 10% neutral buffered formaldehyde prior to further processing.

The peripheral blood smear is remarkable for moderate anisocytosis but rather marked poikilocytosis with numerous teardrop cells and elliptocytes. Notably, the white cells only showed neutrophilic predominance without left shift, dysplasia or circulating blasts/immature cells were present. Platelets were slightly reduced but without significant abnormalities.

The bone core biopsy (figure 1) is markedly hypercellular for age at nearly 80-90%. There are several areas with sheets of monomorphic cells with rather medium-sized hyperchromatic nuclei and scant clear-eosinophilic cytoplasm. Few scattered lymphoid aggregates are present. Amidst the monomorphic areas, there are several scattered megakaryocytes with largely normal morphology. Elsewhere, there are maturing granulocytic cells apparent with scattered erythroid forms. No osteolysis was seen.

The aspirate smears (figure 2) were cellular and the most striking feature was the presence of cells with slightly higher N/C ratio with distinct metachromatic granules (metachromatic blasts) consistent with mast cell lineage comprising up to 10% of all cells. Besides these cells, up to 10% of cells had the cytomorphology of typical myeloblasts with occasional azurophilic granules but basophilic and often vacuolated cytoplasm. Besides these, a subset of cells intermediate in cytomorphology between myeloblasts and metachromatic blasts and mast cells containing metachromatic granules were noted with prominent hemophagocytosis (predominantly red cells) constituting up to 10% of all cells. Besides these, more typical mast cells were present but constituted a minority of cells. Many cells were rather difficult to classify as either mast cells or blasts. Rare dysplastic hypolobated megakaryocytes and rare dysplastic monolobated/bilobated neutrophils were identified but significant dysplasia was lacking. Erythroid precursors however show moderate dysplastic changes (viz. nuclear irregularity with budded nuclei, some megaloblastoid change). Alpha napthyl butyrate esterase identified up to 5% monocytic cells.

Immunohistochemical stain (figure 1) showed few CD34 positive blasts (5% of all nucleated cells). CD117 shows confluent sheets of positive cells on the core biopsy (up to nearly 60% of the cellular elements) with a significant subset of these cells staining positive with mast cell tryptase. These atypical CD117+ cells were also positive for toluidine blue but negative for CD2, CD25, CD30, and CD123. Factor VIII related antigen and CD61 stain shows slightly increased numbers of megakaryocytes without significant clustering. CD20/PAX-5 marked few B-cell clusters. Reticulin stain shows a focal mild increase in reticulin fibrosis. Iron stain performed on the bone marrow aspirate shows increased storage iron, decreased sideroblastic iron, and no ringed sideroblasts are identified.

Flow cytometric analysis (figure 3) performed on the bone marrow aspirate showed a small myeloid blast population (approximately 2% of all events analyzed), expressing dim CD45, CD34, CD33, CD117, CD33, HLA-DR, dim CD4, and CD38.

In addition, there was also an abnormal population expressing dim CD45 with high side scatter characteristics, expressing CD33, CD13, CD117, CD4, CD56 (subset), and CD38; these immature cells were negative for CD34.

In addition, there was a small monoclonal B-cell population (approximately 1.5% of all events analyzed), expressing bright CD45, CD19, dim CD20, dim CD5, dim CD22, CD23, CD38, HLA-DR, with dim surface kappa light chain restriction consistent with a MBL-type CLL immunophenotype.

Abnormal complex male karyotype (33,Y,-X,+add(1)(p22),add(1)(q21),-2,-4,-5,-6,-7,-8,+9,-10, -11,-12,-13,add(13)(q22),-14,add(14)(p11.2),-15,-16,-17,-18, -22,-22,+3mar[1]/62-63,idemx2,+X[1],+X[1],+22, +9-11mar[cp2]/46,XY[17])

FISH studies for BCR-ABL, CHIC2 deletion, PDGFRA, PDGFRB were negative

Sequencing analysis negative for KIT D816V mutation 9 (exon 17) in the marrow aspirate cells. Additional sequencing of the entire KIT genome did not reveal any other mutations.

1. Atypical mast cell proliferation: CD117+ /tryptase+/toluidine blue+ lacking CD2 and CD25, CD30 and KIT mutations.

2. Continuum of atypical cells between myeloid blasts, metachromatic blasts and immature mast cells.

3. Prominent erythrophagocytosis, hitherto not described in mast cell neoplasms.

4. Associated small CLL-like clonal B-cell population, reminiscent of one case of SM-CLL reported by Horny et al. [ref 1]. But the reported case was SM, with CD2+CD25+ KIT mutation with a larger CLL component.

5. Issue of classification:

a. Question of concurrent MDS like RAEB-1/2 especially in view of markedly complex karyotype (could this represent an ASM-MDS) and increased blasts with dysplasia.

b. However, metachromatic immature blasts indicate an immature mast cell process supporting either aleukemic Mast cell leukemia (aMCL)1 or myelomastocytic leukemia (MML).

c. MML seems the best fit given the complex karyotype and negative KIT mutation.

This case most closely resembles one described by Wimazal et al in 1999 of a MML with associated RAEB evidencing complex karyotype and negative KIT mutation presenting with hyperfibrinolysis.(ref.4)

Figure Legend

Fig 1:

A and B. Bone core biopsy showing hypercellular marrow for age with a monomorphous infiltrate. These areas showed some streaming of polygonal cells but obvious spindly morphology was not apparent. C, Other areas with intact trilineage hematopoiesis including several megakaryocytes. D, CD34 showing increase vasculature without significant increase in the blast population. E. CD117 with sheets of positive cells; adjoining lymphoid aggregate at top left negative for CD117. A significant subset of CD117+ cells staining positive with mast cell tryptase. (F). CD2 (G) and MPO (H) are both negative in the CD117+ cells. CD2 additionally marks T-cells. In addition, there is only mild increase in reticulin fibrosis (I)

Fig 2:

A, Aspirate smears showing increased mast cells with metachromatic granules. B, Other areas with agranular blastic cells. Eosinophils were not increased and showed normal morphology. C, Prominent erythrophagocytosis in immature cells with metachromatic granules. D, Aspirate smears showing erythroid forms with nuclear budding and megaloblastoid change indicative of dyserythropoiesis.

Fig 3: Flow cytometry demonstrating mast cell component expressing dim CD45, high side scatter with CD117+CD13+CD33+ while the CLL component in the lymphocyte gate expressed CD19+¬CD5+CD23+ with dim kappa expression. Although not depicted, another small myeloid blast population was present in the typical 'blast gate' of dim CD45/low side scatter.

REFERENCE:

1. Horny HP, Sotlar K, Stellmacher F, Valent P, Grabbe J. An unusual case of systemic mastocytosis associated with chronic lymphocytic leukaemia (SM-CLL). J Clin Pathol. 2006 Mar;59(3):264-8.

2. Joris M, Georgin-Lavialle S, Chandesris MO, Lhermitte L, Claisse JF, Canioni D, Hanssens K, Damaj G, Hermine O, Hamidou M. Mast Cell Leukaemia: c-KIT Mutations Are Not Always Positive. Case Report Hematol. 2012;2012:517546.

3. Arredondo AR, Gotlib J, Shier L, Medeiros B, Wong K, Cherry A, Corless C,

Arber DA, Valent P, George TI. Myelomastocytic leukemia versus mast cell leukemia

versus systemic mastocytosis associated with acute myeloid leukemia: a diagnostic challenge. Am J Hematol. 2010 Aug;85(8):600-6.

4.Wimazal F, Sperr WR, Horny HP, et al. Hyperfibrinolysis in a case of myelodysplastic syndrome with leukemic spread of mast cells. Am J Hematol 1999;61:66–77.

Acute myeloid leukemia with mast cell features, most consistent with myelomastocytic leukemia (MML), KIT mutation negative

Aggressive systemic mastocytosis with associated clonal hematological non-mast cell lineage disease (refractory anemia with excess blasts-2 and monoclonal B-cell lymphocytosis)

Case 391