Case 10 -
Myeloid Sarcoma with Mast Cell and Megakaryocytic Differentiation
Elaine S. Jaffe
National Cancer Institute
NIH, Bethesda, MD
Click on each slide thumbnail image for an enlarged view
A 51 year old female had a history of systemic mastocytosis associated with a myelodysplastic
syndrome. She underwent an HLA-matched peripheral blood stem cell transplant. Approximately 3 years
later she developed an scalp mass. A biopsy was obtained.
Case 10 - Figure 1 - A skin biopsy from 2001 shows infiltration of the dermis by atypical mast cells with a polygonal appearance.
Case 10 - Figure 2 - The mast cells are strongly positive for tryptase by immunohistochemistry
Case 10 - Figure 3 - In 2004, following bone marrow transplantation, the patient developed a scalp mass. Deep dermis and subcutaneous tissues are infiltrated by large blastic cells. Rare eosinophilic myelocytes are identified.
Case 10 - Figure 4 - The scalp mass also contains giant cells suggestive of megakaryocytes.
Case 10 - Figure 5 - Many of the blastic cells are positive for chloroacetate esterase, but negative for myeloperoxidase (not shown).
Case 10 - Figure 6 - The megakaryocytes show staining for p-selectin.
In recent years, systemic mastocytosis (systemic tissue mast cell disease) has been recognized as one
of the myeloproliferative disorders, in which multiple cell lineages may be involved  . Patients may
show evidence of a myeloproliferative disorder at presentation, or a systemic myeloproliferative disorder
may evolve during the patient's course. Cutaneous involvement is common in patients with systemic tissue
mast cell disease  . Normal mast cells express chloroacetate esterase, tryptase and c-kit (CD117) .
They are negative for myeloperoxidase. In systemic mastocytosis the mast cells may show aberrant
expression of CD2 and CD25  .
Myeloid sarcoma is a proliferation of immature cells of myeloid origin occurring outside the bone
marrow, or as a mass lesion in a bony site. Synonyms include extramedullary myeloid tumor, granulocytic
sarcoma, and the older term, chloroma, which is derived from the green color seen grossly in those
lesions composed of immature neutrophils  . Myeloid sarcomas can be derived from immature cells of
diverse lineages, including granulocytes, eosinophils, monocytic cells, and megakaryocytes. Tumors with
erythroid differentiation are rare. In patients with underlying mast cell disease, immature mast cells
may be present  .
Myeloid sarcomas can be associated with many types of bone marrow disorders. They may precede or
occur concurrently with acute or chronic myeloid leukemia, myeloproliferative disorders, and
myelodysplastic syndromes. Extramedullary tumors are somewhat more common with acute monoblastic
leukemias, and skin is a common site of involvement. Cutaneous lesions may be the initial manifestation
of acute monoblastic leukemia. Myeloid sarcomas may also be the primary evidence of relapse following
therapy. The development of a myeloblastic tumor in someone with chronic myelogenous leukemia is
evidence of blastic transformation.
In the WHO classification  , myeloid sarcomas are classified according to lineage and also the
stage of differentiation. There are three major types: 1) blastic; 2) immature; and 3) differentiated.
As the names imply, blastic tumors are composed primarily of blasts. In immature lesions, a combination
of blasts and immature myeloid precursors is seen. In the differentiated form, maturation to mature
neutrophils and other elements is seen.
Useful immunohistochemical or enzyme cytochemical stains include myeloperoxidase (MPO), performed as
an enzymatic or immunohistochemical stain; chloroacetate esterase (Leder stain); CD68, and c-Kit
CD99 may be positive, but is also positive in lymphoblastic malignancies, and of course, PNET/
Ewing's sarcoma  . CD43 is consistently present but does not have lineage specificity. P-Selectin
may be positive in cells showing megakaryocytic differentiation. Lymphoid markers such as CD3, CD20 and
TDT should be negative, but CD7, CD2, and CD56 may be expressed in some very immature myeloid tumors
A somewhat related phenomenon is the tumor of "plasmacytoid monocytes" often seen in association with
chronic myelomonocytic leukemia (CMML)
. These tumors are thought to be related to dendritic
cells, and are clonally related to the underlying CMML. Lymph node is the most common site of
involvement, but these lesions can also be identified in cutaneous sites.
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