Submitting Author: Reichard, Kaaren Kemp, MD
Institution: Mayo Clinic Rochester
Additional authors:Dr. Min Yan and Dr. Michael Pennington, Indiana University Health, Goshen Hospital
Session: Extramedullary manifestations of myeloid neoplasms

The patient is a 79 year-old male. By report, he had a history of CML. However, later, based on the findings in the bone marrow we were able to clarify a history of CMML (diagnosis rendered elsewhere, duration unknown).

The patient was noted to have right chest wall lymphadenopathy and underwent an excisional biopsy.

Two weeks later, a bone marrow biopsy was performed due to en elevated white blood cell count.

Lymph node, right chest wall: A portion of the fresh specimen was submitted for flow cytometric analysis. The remainder of the specimen was fixed in formalin.

The lymph node was enlarged and demonstrated partial effacement of normal nodal architecture by a prominent interfollicular infiltrate. The interfollicular infiltrate was composed of an essentially monotonous population of intermediate to large size cells with blastic chromatin, round to slightly irregular nuclear contours and a moderate rim of lightly eosinophilic cytoplasm. In various foci, greater or lesser numbers of admixed stromal cells, dendritic cells and macrophages were observed. There was no admixture of erythroid precursors, megakaryocytes or maturing granulocytic elements. The residual follicular areas showed an occasional germinal center but were otherwise composed of small, mature-appearing lymphocytes.

Peripheral blood and bone marrow biopsy:

Peripheral blood:

CBC: The hemoglobin is 10.6 g/dl, platelet count 29 x 10^9 /L and white blood cell count 50.6 x 10^9 /L.

Differential cell count: neutrophils 47%, lymphocytes 5%, monocytes 28%, basophils 2%, metamyelocytes 3%, myelocytes 7%, blasts 8%.

Morphology: The red blood cells are decreased in number with mild anisopoikilocytosis including rare elliptocytes and other unusually-shaped cells. There is minimal polychromasia. The white blood cells are increased in number and show a granulocytic leukocytosis with left shift including 8% blasts. A subtle basophilia is observed. The granulocytes demonstrate dysplastic features including hypogranularity. Monocytic cells are increased with abnormal nuclear folding and chromatin.

Bone marrow aspirate:

The bone marrow aspirate was adequate for cell evaluation and enumeration.

Bone marrow differential (500-cell/unit prep): neutrophils (segs and bands) 24; metamyelocytes 3, myelocytes 12; promyelocytes 2, blasts/promonocytes 24; normoblasts 11; monocytes 20; lymphocytes 4.

Morphology: The erythroid series demonstrated progressive maturation with unremarkable morphology. The granulocytic series demonstrates progressive maturation, but was slightly left-shifted with dysplastic features including hypogranularity and abnormal nuclear segmentation. Increased blasts are noted and are characterized by a small to medium size, blastic chromatin, variably prominent nucleoli, and a moderate rim of basophilic cytoplasm. An increase in monocytic cells is appreciable, with scattered cells meeting criteria for promonocytes.

Overall the blast/blast equivalent count is 24% meeting WHO 2008 criteria for acute myeloid leukemia. Megakaryocytes showed predominantly normal morphology. The constellation of findings raised the possibility of a background of chronic myelomonocytic leukemia (which was subsequently confirmed by discussion with the medical oncologist).

Bone marrow clot section/trephine biopsy: Essentially inadequate, containing only a few small particles of bone marrow. The few particles of bone marrow were hypercellular with a predominance of left-shifted granulocytes, admixed monocytes and lacking clear-cut evidence of sheets of blasts. Megakaryocytes and erythroid elements appear decreased.

Right chest wall lymph node:

Flow cytometric analysis showed a monoclonal B-cell population lacking CD5 and CD10 expression comprising approximately 16% of total analyzed events. There was no abnormal T-cell population. Antigens tested: CD3, CD5, CD7, CD10, CD19, CD20, CD45, kappa and lambda. Upon review of the lymph node showing a prominent interfollicular infiltrate, the histograms were re-reviewed. A prominent population of cells (25-30%) are present and (as expected) show no staining for any of the markers that were tested except dim CD45.

Immunohistochemical studies were performed using antibodies against CD3, CD14, CD20, CD34, CD68, CD117 (KIT), BCL6, cyclin D1, lysozyme and myeloperoxidase. CD34 reveals a mild increase in vessels but no increase in CD34-positive cells.

Interfollicular infiltrate: KIT highlights the majority of the mononuclear cells. A two-tier staining pattern is observed with the majority showing weak positivity and occasional cells showing stronger membrane intensity. Myeloperoxidase appears to stain approximately 20% of the mononuclear cells and the pattern seems to correlate with the stronger staining CD117 positive cells. Lysozyme is difficult to interpret but demonstrates staining of at least 50% cells. CD68 highlights background macrophages. CD14 stains a small subset (10-20%). This immunohistochemical profile, in conjunction with the morphology, indicates a myeloid sarcoma with monocytic differentiation.

Follicular regions: CD20 highlights the vast majority of the small lymphocytes. There are also occasional scattered CD20 positive B-cells in the paracortical region but the majority of the larger cells in the interfollicualr area are negative. The CD20 positive B-cells are negative for CD10, BCL-6, and cyclin D1. BCL-6, similar to the slide submitted by the referring institution, shows a prominent staining of the interfollicular large cells. BCL-2 is positive in the lymphoid cells but negative in the germinal center cells. CD3 highlights occasional small, residual T-cells.

The predominant CD20-positive aggregates of small B-cells, in conjunction with flow cytometry, indicate minimal involvement by a low-grade B-cell lymphoma lacking CD5 and CD10 expression. There are no morphologic features of a large cell component.

Bone marrow:

Flow cytometric analysis showed no increase in CD34 or CD117 positive blasts, no monoclonal B or abnormal T-cell population. An increase in monocytic cells (approximately 30%), as defined by bright CD33, CD15 and scatter properties, was noted.

Immunohistochemical studies were performed on the limited clot section using antibodies against CD34, CD68, CD117, lysozyme and myeloperoxidase. CD34 does not reveal a significant increase in CD34-positive blasts. CD68 highlights approximately 40-50% of the mononuclear cells. CD117 stains a slight increase in positivity in the mononuclear cells, but distinguishing blasts from erythroid precursors, granulocytic precursors, and abnormal monocytic myeloid cells is problematic. Lysozyme is diffusely positive in the mononuclear cells. Myeloperoxidase stains approximately 50% of the mononuclear infiltrate.

Cytochemistry on the aspirate smear for butyrate esterase (brown) and chloroacetate esterase (CLE) (blue). Butyrate esterase shows approximately 50% of the cells to be of monocytic derivation. This includes a subset of the blasts identified morphologically. The remaining blasts and left-shifted granulocytic elements are CLE positive.

Bone marrow aspirate: normal male karyotype.

Not performed

1) Discordance of disease presentation in the bone marrow (CMML with overall relatively low blast count and background maturation) versus the right chest wall mass (sheets of blasts).

2) Immunohistochemical discrepancy between the monocytic and myeloid blasts in the lymph node (weakly positive and strongly positive for CD117, respectively) and the bone marrow (no significant weakly positive CD117 population, although pockets of monocytic blasts clearly present on aspirate smear).

3) BCL6 positivity in many of the paracortical blasts, in conjunction with the flow cytometric findings of a monoclonal B-cell population, led to a misinterpretation of the paracortical cells as diffuse large B-cell lymphoma.

Lymph node, right chest wall, excisional biopsy:

1) Myeloid sarcoma with monocytic differentiation.

2) Minimal involvement by low-grade B-cell lymphoma.

Bone marrow aspirate and clot section:

1) Increased blasts (approximately 25%) meeting criteria for acute myeloid leukemia arising in a background of chronic myelomonocytic leukemia.

Blast phase of chronic myelomonocytic leukemia involving bone marrow and right chest wall lymph node (myeloid sarcoma); minimal low-grade B-cell lymphoma involving lymph node

Case 59