ANATOMIC PATHOLOGY
Original Article
Ossifying Fibromyxoid Tumor of Soft Parts
Additional Observations of a Distinctive Soft Tissue Tumor
MARKKU MIETTINEN, M.D.
The author studied four subcutaneous soft tissue tumors, similar
to those recently described by Enzinger and associates (Am J
Surg Pathol 1989;13:817) by the name "ossifying fibromyxoid
tumor," by immunohistochemistry and electron microscopy to
further understand the cellular nature of this lesion. The four
tumors were composed of uniform round cells often surrounded
by a lacunar space. The tumors often contained a peripheral
zone of metaplastic bone. The cellularity was high, but the mitotic
rate was low, suggesting a benign or borderline nature of the
lesion. Longer follow-up was available for three cases, showing
recurrence-free survival times of 11, 8, and 3 years. Immunohistochemistry studies revealed that all tumors were strongly
positive for S-100 protein and focally positive for Leu-7, whereas
melanoma-specific marker HMB4S was negative. Vimentin was
the main type of intermediate filament protein, and one case also
contained scattered glial fibrillary acidic protein-positive cells.
Epithelial markers (keratins, epithelial membrane antigen),
desmin, and muscle actins were negative. Electron microscopic
examination showed partial, sometimes reduplicated, basal lamina surrounding many cells. Complex cell processes were also
present. No myofilaments were found. The immunohistochemical
and electron microscopic results may suggest that this tumor
has Schwann's cell differentiation. (Key words: Soft tissue tumor;
Nerve sheath; Schwann's cell; Chondroid neoplasm; Immunohistochemistry; Electron microscopy) Am J Clin Pathol 1991;95:
142-149
Enzinger and associates' recently described a distinctive
soft tissue lesion, which they named ossifying fibromyxoid
tumor of soft parts. During the last few years, I have identified four cases of morphologically similar neoplasms,
which have also been studied by immunohistochemistry
and electron microscopy. The purpose of this article is to
describe four cases of this tumor type in an attempt to
increase understanding of its cellular nature.
two as soft tissue tumors of unknown histogenesis with
possible low-grade malignant potential. Hematoxylin and
eosin, periodic acid-Schiff (PAS), and Alcian blue stains
at pH 1.0 (HC1) and 2.5 (acetic acid) were performed.
Immunohistochemistry
Studies
Formaldehyde-fixed and paraffin-embedded tissue of
each case was studied. The antibodies and their sources
and dilutions are shown in Table 1. The immunostaining
MATERIALS AND METHODS
was performed with the avidin-biotin complex immunoperoxidase technique. For the immunostaining of inCases
termediate filament proteins (except for glial fibrillary
Four soft tissue tumors representing a recently described
acidic protein [GFAP]), epithelial membrane antigen
entity, ossifying fibromyxoid tumor of soft parts, were
(EMA), and S-100 protein, a light protease treatment was
studied. One of these cases had been originally diagnosed
applied before the primary antibody. The enzyme was a
as clear cell sarcoma, one as proliferative fasciitis, and
0.05% (weight/volume [w/v]) crude powder of pepsin
(2,500 U/g; Merck & Company, Darmstadt, Germany)
in distilled water, acidified with HC1 to pH 1.8-2.0. The
treatment
time was 10-30 minutes (several digestion times
From the Department of Pathology. University of Helsinki, Helsinki,
Finland, and the Department of Pathology and Cell Biology, Thomas
for the specimens were done in parallel), and the reaction
Jefferson University, Philadelphia, Pennsylvania.
temperature was 37 °C. Biotinylated goat-antirabbit or
rabbit antimouse IgG antibodies were used, with the exReceived February 23, 1990; accepted for publication March 27, 1990.
Supported in part by the Finnish Cancer Research Fund.
ception that a biotinylated rabbit antimouse IgM antibody
Address reprint requests to Dr. Miettinen: Department of Pathology
was used for the immunostaining of Leu-7. The color was
and Cell Biology, Pavilion 402, Thomas Jefferson University, 1025 Waldeveloped
with aminoethylcarbazole or diaminobenzidine
nut Street, Philadelphia, Pennsylvania 19107.
142
143
MIETTINEN
Ossifying Fibromyxoid Tumor of Soft Parts
TABLE 1. ANTIBODIES USED IN THE CHARACTERIZATION OF THE TUMORS
Designation of the Antibody and Description
of its Specificity, Abbreviation
Monoclonal antibodies
CAM5,2 (Cyto)keratins of 40, 45, and 52 kD
(Ker)
Vimentin, V1M-3B4 (Vim)
Desmin (Des)
Glial fibrillary acidic protein (GFAP)
HMB-45, melanoma-specific antibody (Mel)
Epithelial membrane antigen (EMA)
Leu-7
Muscle-specific actins (HHF 35)
Rabbit antisera to
S-100 protein (of bovine origin) (S-100)
Dilution
Reference
Source
17
Becton Dickinson, Mountain View,
California
Courtesy of Professor Werner W. Franke
Biogenex
Amersham, Little Chalfont, United Kingdom
Dakopatts, Glostrup, Denmark
Enzo-Biochem
Dakopatts
Becton Dickinson
Enzo-Biochem, New York, New York
1:15
2
1:1,000
1:1
1:10
1:100
1:1,600
1:50
1:4
1:2,000
5
3
1:400
Dakopatts
supplemented with 0.02% (w/v) hydrogen peroxide. Positive controls were run for each marker. Negative controls
in each case failed to produce immunostaining.
tumor nodules were sharply demarcated from the surrounding tissues.
Light Microscopic Examination
Electron Microscopic Examination
Of two cases, formaldehyde-fixed material was postfixed
with 2.5% (volume/volume [v/v]) phosphate-buffered
glutaraldehyde and further with 1% (w/v) osmium tetroxide, and embedded in LX-112 resin. The thin sections
were stained for contrast with uranyl acetate and lead
citrate. Of two cases, material was obtained from paraffin
blocks, deparaffinized, rehydrated, and then treated as described above.
RESULTS
Clinical Features
The clinical features have been summarized in Table
2. The age range of the patients was 39-86 years, and
three of the patients were women. None of the patients
had von Recklinghausen's disease. All tumors were discrete subcutaneous nodules measuring 1-7 cm in diameter
(mostly 2 cm or less). One patient had a group of lesions
at the same site. Three of the tumors were small enough
to be locally excised in minor health centers. Because one
of the tumors was originally diagnosed as a clear cell sarcoma (case 1), this patient obtained postoperative local
radiation therapy. In the other cases, no oncologic treatment was given. Follow-up times of 11, 8, 3, and 1 years
have revealed no recurrences or metastases.
Gross Features
The tumor tissue was gray-white and mostly soft. Three
of the cases contained harder foci of cartilage-like consistency. One tumor contained a peripheral shell of calcified
tissue, microscopically representing metaplastic bone. The
All tumors were surrounded by a thick collagenous
capsule bordering the subcutaneous fat (Fig. 1). However,
the capsule was disrupted by infiltrative tumor cell nests
in three of four cases. Scattered lymphocytes and plasma
cells were often found in the most remote infiltrative cell
nests, which seemed to form around delicate vessels. The
periphery of the tumors often had thick collagenous septa
lobulating the solid areas of neoplastic cells. In two cases,
the neoplasm was partially surrounded by trabeculae of
metaplastic bone (Fig. 2). In some parts of the tumors,
sclerotic areas were merging with the cellular areas (Fig.
3). None of the tumors was associated with recognizable
nerve structures.
The cellularity was high and the tumor cells were relatively uniform. The nuclei were small to medium-sized,
round or oval with inconspicuous nucleoli and low overall
chromatin density. In many areas of each tumor, the cells
had a clear cytoplasmic appearance with often indistinct
cellular borders. In some areas of the tumors, the cyto-
TABLE 2 . BASIC CLINICAL D A T A OF THE FOUR
OSSIFYING FIBROMYXOID T U M O R S
Case
Age (years)
Sex
1
39/M
2
61/F
3
86/F
4
58/F
Vol. 95 • No. 2
Tumor Location and Size
Follow-up
Proximal thigh, multiple
subcutaneous nodules, up to 2
cm in diameter
Subcutaneous, unknown site, 1.5
cm in diameter
Shoulder, subcutaneous + fascial,
7 cm in diameter
Thoracic wall, subcutaneous, 1.5
cm in diameter
8 years,
alive, well
3 years,
alive, well
11 years,
alive, well
1 year,
alive, well
144
ANATOMIC PATHOLOGY
Original Article
FIG. 1 (upper, left). The tumor is surrounded by a thick collagenous capsule and is bordered by subcutaneous fat. The periphery
of the tumor is less cellular and contains hyalinized areas and spicules of metaplastic bone. Case 3.
FIG. 2 (upper, right). The tumor contains an island of mature metaplastic bone. Note the uniform and
clear cytoplasmic round cell pattern. Case 2.
A.J.C.P. • February 1991
145
MIETTINEN
Ossifying Fibromyxoid Tumor of Soft Parts
FIG. 3 (lower, left). The tumor contains sclerotic areas merging with the highly cellular tissue of round clear cell areas
with lacunar pattern. Case 2.
FIG. 4 (lower, right). The tumor cells are uniform and have a clear or eosinophilic cytoplasm. Note that the lacunar
appearance results, in part, from the presence of wide intercellular spaces. Case 1.
<
plasm was eosinophilic, but the tumor still had a clear
cell or lacunar appearance because of the presence of wide
pericellular spaces (Figs. 3 and 4). All tumors were rich
in capillary vessels that often had hyalinized walls. In some
areas of two cases, the tumor cells were arranged in trabecule in a myxomatous stroma resembling the pattern
seen in extraskeletal myxoid chondrosarcoma (Fig. 5). The
mitotic count was low (1-2 mitoses/10 high-power fields).
No atypical mitoses were found. Small central necroses
or necrobiotic cystic areas were found in two tumors. PAS
stain did not reveal cytoplasmic glycogen. The four tumors
showed much less Alcian blue positivity at pH 1.0 and
with 0.5 mol/L, as compared with denned chondroid tumors.
Immunohistochemistry
Studies
The immunohistochemical findings have been summarized in Table 3. Prominent vimentin immunoreactivity was found in each case in most of the neoplastic
cells with the use of two different antibodies to vimentin
(Fig. 6A). All tumors were strongly positive for S-100 protein (Fig. 6B). In one case, scattered GFAP-positive cells
were present (Fig. 6C). Leu-7 immunoreactivity was
found in one case in a prominent pattern (Fig. 6D). In
two of three cases, only single scattered cells (about 1%
of tumor cells) were Leu-7 positive. Cytokeratin, desmin,
and EMA immunostainings were negative. All tumors
were negative for HMB45, a melanoma marker. Muscle
actin immunoreactivity was found in vascular pericytes
in all tumors (Fig. 6E), and in two tumors some spindle
cells in the sclerotic areas were positive. It was not possible
to determine with certainty whether the positive cells belonged to the neoplastic population or were nonspecific
stromal cells.
Electron Microscopic Examination
All tumor showed basically similar ultrastructural features, although in two cases only embedded and reprocessed material was available, and therefore only a limited
number of features could be identified. The neoplastic
cells had round or oval nuclei with few indentations and
an even chromatin pattern with small nucleoli. A welldeveloped partial, at some places reduplicated, basal lamina surrounded many but not all tumor cells (Fig. 7). The
tumor cells typically had numerous profiles of rough endoplasmic reticulum, often with cisternal dilatations. Mitochondria were seen in moderate numbers. A remarkable
TABLE 3. IMMUNOHISTOCHEMICAL FINDINGS
IN THE FOUR OSSIFYING FIBROMYOXOID
TUMORS OF SOFT TISSUES
Case
1
2
3
4
FIG. 5. Some areas of the tumors show a trabecular
pattern with myxomatous stroma. Case 3.
Vim Ker S-100
3+
3+
3+
3+
0
0
0
0
3+
3+
3+
3+
Leu-7
1+
1+
0
3+
GFAP Met
0
0
1+
0
0
0
0
0
Des EMA
0
0
0
0
0
0
0
0
Muscle
Actins
0
0
0
0
The antibody abbreviations are as in Table I.
The results have been quantified as follows: 0 = negative: 1+ less than 10% of tumor cells
positive; 2+ 10-50% of tumor cells positive: 3+ more than 50% of tumor cells positive.
Vol. 95 • No. 2
146
ANATOMIC PATHOLOGY
Original Article
FlG. 6. Immunohistochemicalfindingsof the ossifyingfibromyxoidtumor. A (upper, left). All tumor cells are positive for vimentin. B (lower, left).
The tumor cells are positive for S-100 protein. C(upper, right). Scattered tumor cells (arrows) are GFAP positive. D (center, right). Leu-7 immunoreactivity
is present in a patchy pattern in one tumor. E (lower, right). Muscle actin immunoreactivity is seen in pericytes but not in the tumor cells.
feature seen in many cells in all cases was the presence of
prominent arrays of intermediate filaments without any
structural organization (Fig. 8). Microfilaments could not
be specifically identified, and, especially, there were no
signs of muscle cell type filaments. Some cells had occa-
sional pinocytotic vesicles at the plasma membrane. Many
cells had uneven contours with irregular elongated processes. Some cell processes were enveloped with multiple
layers of basal lamina material (Fig. 9). In one case, occasional primitive (intermediate) junctions were present.
A.J.C.P. • February 1991
MIETTINEN
Ossifying Fibromyxoid Tumor of Soft Parts
147
V.^3-
r \
FIG. 7 (upper). Electron microscopy shows tumor cells rich in rough endoplasmic reticulum, mitochondria, and intermediate filaments.
Also, note partial focally reduplicated basal lamina (arrows) (X6,400).
FlG. 8 (lower). A higher electron microscopic magnification shows parallel arrays of intermediate filaments,
which upon immunostaining appeared to consist of vimentin (X26.000). Case 2.
Vol. 95 • No. 2
148
ANATOMIC PATHOLOGY
Article
FIG. 9. By electron microscopy, many tumor cells have elongated cell
processes covered by multiplicated basal laminae (XI5,300). Case 2.
Glycogen particles were not identified with certainty. The
intercellular spaces commonly contained collagen fibers.
DISCUSSION
This study examined four histologically similar soft tissue tumors that appeared identical to the tumor entity
recently described and named "ossifying fibromyxoid tumor of soft parts" by Enzinger and associates.' These tumors were highly cellular round cell lesions, often having
a peripheral rim of metaplastic bone. Clinicopathologically, the tumors resembled those described by Enzinger
and associates' by being mostly small superficial subcutaneous tumors in the trunk or extremities of adult patients. All tumors described in the current study were benign. However, the spectrum of ossifying fibromyxoid tumor may include malignant variants with potential for
recurrence and metastasis.' However, the taxonomic position and diagnosis of such histologically malignant tumors can be interpreted differently; these tumors may also
be classified as extraskeletal osteosarcomas, as also discussed by Enzinger and associates.' We excluded two such
overtly sarcomatous tumors with abundant mitoses from
this report.
The emphasis of this work was to determine the cellular
differentiation properties of the ossifying fibromyxoid tumor and to discuss its possible relationship with known
tumor entities. The relationship of this tumor to
Schwann's cell and chondroid tumors especially deserves
attention in view of the immunohistochemical and elec-
A.J.C.P. •
tron microscopic findings. Because of its morphologic
characteristics and location, the relationship to clear cell
sarcoma, skin adnexal tumors, and nerve sheath myxoma
also must be considered.
Some ultrastructural features of ossifying fibromyxoid
tumor— namely well-developed, although partial, basal
lamina on many tumor cells, and the presence of complex
cell processes surrounded by a basal lamina—resemble
those observed in benign nerve sheath tumors, especially
in schwannoma.3,4 Partial basal laminas are also typical
of many malignant Schwann's (nerve sheath) cell tumors
and may reflect incomplete Schwann's cell differentiation.3'5 Many immunohistochemical findings of this tumor have features compatible with Schwann's cell differentiation because of the strong and uniform vimentin and
S-100 protein positivity, as typically seen in schwannomas.6'7 Focal GFAP immunoreactivity found in one of
the cases also has been found in Schwann's cell tumors.6,8'9
Leu-7 immunostaining, although not found in all cases,
is also a feature compatible with Schwann's cell differentiation, 10 although Leu-7 is not specific for Schwann's
cell differentiation and has been described in tumors of
non-Schwann's cell lineage, such as leiomyosarcoma and
synovial sarcoma.10 However, none of the tumors examined in this study were either grossly or microscopically
associated with nerves. Furthermore, ossifying fibromyxoid tumor does not resemble any previously described
variant of Schwann's cell neoplasms by light microscopic
examination." These findings make it difficult to state
that this lesion is a Schwann's cell tumor.
The presence of cartilage-like areas with lacuna-like
shrinkage spaces around tumor cells and some areas resembling extraskeletal myxoid chondrosarcoma also necessitate consideration of cartilaginous differentiation of
ossifying fibromyxoid tumor. S-100 protein immunoreactivity, as found in ossifying fibromyxoid tumor, is
also present in chondroid tumors.12 However, it is unlikely
that the main components of the tumor are cartilage related. The electron microscopic appearance with prominent basal lamina on many tumor cells clearly speaks
against cartilaginous differentiation; chondroid tumors do
not show basal lamina.13"15 Cells of differentiated cartilaginous tumors also often contain abundant glycogen,1415
not found in the tumors of the current investigation by
histochemical or electron microscopic methods. The
presence of metaplastic bone can be a histogenetically
nonspecific phenomenon because osseous metaplasia is
commonly seen, for example, in scar tissue. At present,
no well-documented immunohistochemical markers are
available for determining chondroid or osseous differentiation in formaldehyde-fixed and paraffin-embedded
tissue.
1991
149
MIETTINEN
Ossifying Fibromyxc Tumor of Soft Parts
Clear cell sarcoma16 is a tumor entity whose relationship
with the ossifying fibromyxoid tumor should be considered. Common to both of these entities are the clear cell
appearance and the S-100 positivity.17 However, the basic
structure of these tumors is different. Although clear cell
sarcoma has distinct fine lobulation, the lobulation seen
in ossifying fibromyxoid tumor is coarser and the lobules
are typically separated by thick collagenous septa. The
cytologic picture is also different. Clear cell sarcoma has
large nuclei and usually large nucleoli, 1617 whereas ossifying fibromyxoid tumor has small nuclei and inconspicuous nucleoli. Furthermore, clear cell sarcoma, now generally regarded as a soft tissue analog to malignant melanoma, is positive for a melanoma-specific antigen,
HMB45, 18 unlike ossifying fibromyxoid tumor. Some
clear cell sarcomas with prominent basal laminas have
been found by electron microscopic examination, thus
resembling Schwann's cell tumors. This finding may also
illustrate their remote relationship to Schwann's cell tu19
mors.
Because of the relatively superficial location and osteocartilaginous features of the ossifying fibromyxoid tumor,
its possible relationship to mixed tumor (pleomorphic adenoma) of the sweat glands also merits consideration. The
total lack of any morphologically evident epithelial differentiation and the absence of the epithelial markers,
most significantly keratins, do not prove that ossifying
fibromyxoid tumor would be related to skin adnexal tumors.
The lobulation of ossifying fibromyxoid tumor and the
focal myxoid appearance show some similarity to dermal
nerve sheath myxoma, which is also S-100 protein
positive20 and is related to Schwann's cell neoplasms."' 20
However, nerve sheath myxoma is more superficially located and has a loose, uniformly myxoid appearance. The
presence of sclerotic areas and metaplastic bone is not
typical of nerve sheath myxoma.
In conclusion, immunohistochemical and electron microscopic studies suggest that the ossifying fibromyxoid
tumor of soft parts may be related to Schwann's cell neoplasms. Additional studies are necessary to determine how
and why osseous differentiation is linked with Schwannlike features in ossifying fibromyxoid tumor.
Acknowledgment. The author thanks Albert Kovatich, M.S., for skillful
technical assistance.
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