Histiocytic sarcoma: a study of five cases
including the histiocyte marker CD163
Jeffrey A Vos1, Susan L Abbondanzo1, Carol L Barekman1, JoAnn W Andriko3,
Markku Miettinen2and Nadine S Aguilera1
1Department of Hematopathology, Armed Forces Institute of Pathology, Washington, DC, USA;2Department
of Soft Tissue Pathology, Armed Forces Institute of Pathology, Washington, DC, USA and3Deparment of
Pathology, Walter Reed Medical Center, Washington, DC, USA
Histiocytic sarcoma (HS) is a rare but controversial hematopoietic neoplasm. In the past, malignancies have
been misclassified as histiocytic tumors due to overlapping histologic features and inadequate phenotypic
data. CD163, a recently characterized hemoglobin scavenger receptor, appears to be a ‘specific’ marker of
histiocytic lineage and a promising diagnostic tool for evaluating histiocytic neoplasms. Five cases of HS were
studied to further elucidate the clinicopathologic features of these rare tumors and to demonstrate the
diagnostic utility of CD163. Criteria for diagnosis included histologic and immunohistochemical evidence of
histiocytic differentiation, CD45 positivity, and exclusion of lymphoid, epithelial, melanocytic and dendritic cell
phenotype. Sites of disease included the colon (two cases), palate, inguinal lymph node, and testis. The clinical
course was aggressive in 4/5 patients (survival¼2–15 months). One patient with localized disease of the palate,
survived 17 years after diagnosis. All patients with poor survival had tumors Z3.5cm. Histologically, all cases
showed diffuse architecture with large, discohesive polygonal cells. Spindling of cells was focally noted.
Hemophagocytosis was identified in 3/5 cases. A prominent inflammatory background was present in 4/5
tumors. All cases were immunoreactive for CD45, CD163, CD68, and lysozyme. S-100 was focally positive in 4/5
cases. Antibodies for melanocytic, epithelial, lymphoid, and dendritic cell markers were negative. Molecular
studies showed monoclonal IgH gene rearrangements in three cases. Our findings suggest that HS is an
uncommon neoplasm frequently extranodal in presentation and aggressive in behavior, with rare exceptions.
Stage of disease and possibly tumor size are significant prognostic indicators. Molecular studies remain
controversial in the diagnosis. The morphologic and phenotypic features are relatively uniform; however, the
diagnosis requires exclusion of more common neoplasms by extensive immunophenotypic studies. CD163
appears to be a specific histiocytic marker and is important in establishing the diagnosis of HS.
Modern Pathology (2005) 18, 693–704, advance online publication, 14 January 2005; doi:10.1038/modpathol.3800346
Keywords: histiocytic sarcoma; true histiocytic lymphoma; CD163; immunohistochemistry; gene rearrangements
Histiocytic sarcoma (HS), formerly designated as
true histiocytic lymphoma, consists of exceedingly
rare hematopoietic neoplasms, representing o1% of
all non-Hodgkin’s lymphomas.1,2Many inconsisten-
cies in the terminology and diagnostic criteria of
these lesions have historically complicated their
recognition and characterization. In fact, neoplasms
originally classified as ‘reticulum cell sarcomas’3
and later ‘histiocytic lymphomas’ by Rappaport4
have encompassed a biologically heterogeneous
group of disorders, the majority of which are now
known to be high-grade T- or B-cell, non-Hodgkin
The term ‘histiocytic sarcoma’ was introduced in
1970 by Mathe ´ et al;11however, this and previous
descriptions were based strictly on the histologic
similarities of the cells to macrophages. Since these
original papers, increasing emphasis has been
placed on cytochemical and immunohistochemical
characterization of these neoplasms in an attempt to
establish true histiocytic lineage.12–17This diagnos-
tic challenge is further complicated as it is necessary
to distinguish HS from other histiocytic processes,
both benign and malignant, to include the hemo-
sis,10,18–21and monocytic leukemia.17,19
The diagnosis of HS relies predominantly on
the verification of histiocytic lineage and the
exclusion of other, poorly differentiated, large cell
Received 16 June 2004; revised and accepted 13 October 2004;
published online 14 January 2005
Correspondence: Dr NS Aguilera, MD, Department of Hemato-
pathology, Armed Forces Institute of Pathology, 6825 16th St. NW,
Bldg 54, Rm 2051, Washington, DC 20306-6000, USA.
Presented in part at the 93rd annual meeting of the United States
and Canadian Academy of Pathology, Vancouver, British Colum-
bia, March 6–12, 2004.
Modern Pathology (2005) 18, 693–704
& 2005 USCAP , Inc All rights reserved 0893-3952/05 $30.00
malignancies (ie lymphoma, carcinoma, melanoma)
by way of extensive immunophenotypic investi-
gation. Fulfilling these conditions, particularly
establishing histiocytic differentiation, has been
problematic due to a high incidence of cross-
reactivity of many immunohistochemical antibodies
originally believed to be specific for histiocytes.22–24
The recent characterization of CD163,25,26a hemo-
globin scavenger receptor protein, has offered a
means of identifying histiocytic cells with a greater
degree of specificity and is a promising marker in
the diagnosis of true histiocytic malignancies.
Finally, the contribution of molecular gene rearran-
gement studies as a diagnostic tool for histiocytic
tumors remains unclear.14,27–29
At the present time, the World Health Organiza-
tion defines HS as a malignancy with morphologic
those of mature tissue histiocytes.2Despite the
application of more stringent diagnostic criteria;
however, an increasing number of reports continue
to shed light on these uncommon malignancies.9,30–44
Extranodal presentation is frequent and the clinical
course is generally aggressive. Unfortunately, per-
sistent clinical and histopathologic disparities in
these studies, in addition to the overall rarity of
these neoplasms, have continued to obscure this
diagnosis and prevented a full appreciation of their
clinical behavior. We report the clinicopathologic
features of five cases of HS to further elucidate the
intriguing nature of these rare malignancies and
introduce the application of a novel immunohisto-
chemical marker, CD163, to attempt to verify the
exact lineage of these neoplasms.
Materials and methods
Specimens and Selection Criteria
Five cases of HS were selected from 19 that were
originally diagnosed as ‘histiocytic sarcoma,’ ‘true
histiocytic lymphoma’ or ‘interdigitating dendritic
cell/histiocytic sarcoma’ from the files of the Armed
Forces Institute of Pathology between 1985 and
2001. Most of the excluded cases were reclassified
following immunohistochemical analysis. Three
cases were excluded at the onset of the study
because they lacked paraffin blocks for ancillary
studies. Case inclusion required morphologic and
immunophenotypic features consistent with histio-
cytic lineage (CD68, CD163, lysozyme, MAC387
reactivity) and the absence of immunoreactivity for
an extensive panel of lymphoid, accessory/dendritic
cell, epithelial, and melanocytic markers. Cases not
meeting these criteria, and those that lacked CD45
(LCA) expression, were excluded. In addition,
patients with a leukemic or widely disseminated
initial presentation were not considered in the
Medical records were retrieved for all cases in this
study. Available records were reviewed for clinical
presentation, tumor size, stage, treatment, and
Histology and Immunohistochemistry
Hematoxylin–eosin slides were reviewed in all
cases. An extensive panel of immunohistochemical
antibodies was applied to 4mm, formalin-fixed,
paraffin-embedded tissue sections according to
standard methods. A list of the primary antibodies,
clones, vendors, pretreatment regimens, and work-
ing dilutions used in this study are provided in
Table 1. The sections were deparaffinized and
treated with the specified antigen retrieval method,
followed by overnight incubation with the primary
antibodies at room temperature. Endogenous en-
zyme activity was quenched by treating the tissue
with 3% hydrogen peroxide for 10min. A strepta-
vidin–biotin–peroxidase system (Vectastain Elites
ABC Kit, Vector Laboratories, Burlingame, CA, USA)
with a diaminobenzidine (DAB) chromogen was
then used to develop the stain. Sections were
counterstained with Gill’s hematoxylin, dehydrated
in ethanol and cleared in xylene. Appropriate
positive and negative controls were used for all
Immunohistochemical stains were interpreted as
positive if at least 10% of the neoplastic cells
showed intense immunoreactivity. Specimens were
considered focally positive if immunoreactivity was
identified within the cells of interest but comprised
less than 10% of the tumor. Cell proliferation was
examined by Ki-67 antibody staining.
Gene Rearrangement Studies
Molecular diagnostic studies were performed by
polymerase chain reaction (PCR) for the immuno-
globulin heavy chain (IgH), T-cell receptor b (TCRb)
and T-cell receptor g (TCRg) genes, as previously
described.45–48DNA was extracted from formalin-
fixed, paraffin-embedded tissues in all cases and
purified according to previously published meth-
ods.46,48Consensus primers were used for detection
of IgH chain (FR3A V region and CFW1 J region),
TCRb chain (VJ1, VJ2, D1J2, and D2J2), and TCRg
chain (V2, V3, V4, V8, V9, JGT3, JGT4, and JGT12)
gene rearrangements. PCR analyses were performed
using a Perkin–Elmer Thermal Cycler 9600 (Applied
Biosystems, Foster City, CA, USA) for 40 cycles
using the following parameters: initial 10min
incubation at 941C, denaturation for 1min at 941C,
annealing for 1min at 521C, elongation for 1min at
721C, and a final elongation step for an additional
5min at 721C. All reactions were performed in
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