This document provides an overview of the histological diagnosis of soft tissue tumors. It discusses the World Health Organization classification of soft tissue tumors and covers the major tumor types. It describes the clinical information and morphological features that are important to evaluate. The role of immunohistochemistry is emphasized for determining the cell lineage and making an accurate diagnosis. Novel immunohistochemical markers that are helpful for specific tumor types are also reviewed. The document concludes with a discussion of tumors of uncertain origin that may require immunohistochemistry for diagnosis.

1. APPROACH TO
HISTOLOGICAL
DIAGNOSIS OF SOFT
TISSUE TUMORS
Moderator: Prof. Suresh Babu
Dr. Nishant Taur
Presenter: Meha Gupta

2. CLASSIFICATION(WHO 2013)
• Adipocytic tumors
• Fibroblastic/Myofibroblastic tumors
• Fibrohistiocytic tumors
• Smooth muscle tumors
• Pericytic tumors
• Skeletal muscle tumors
• Vascular tumors
• Gastrointestinal stromal tumors
• Nerve sheath tumors
• Chondro-osseous tumors
• Undifferentiated/Unclassified
• Tumors of uncertain origin

3. INTRODUCTION
WHO CLASSIFICATION OF SOFT TISSUE AND BONE-4TH EDITION
• Benign mesenchymal tumors outnumber sarcomas by a
factor of about 100
• At least 30% of benign soft tissue tumors are lipomas, 30%
are fibrous and fibrohistiocytic, 10% vascular
• 75% of sarcomas are located in extremities, 10% each in
the trunk and retroperitoneum

4. • Clinical features are only occasionally sufficient to
distinguish benign from malignant soft tissue tumors
• Most STSs of extremities and trunk present as painless
incidentally observed masses
• All superficial lesions >5cms and deep seated lesions have
a high probability of being malignant

5. CLINICAL INFORMATION
• Age:
childhood tumors – neuroblastoma, angiomatoid fibrous
histiocytoma
adult tumors - malignant fibrous histiocytoma (unheard
during childhood)
• Location:
deep lesions tend to be malignant
superficial lesion – benign
• Size:
larger tumors tend to be malignant
• Growth pattern:
rapidly growing –malignant
infiltrating – malignant
• Metastasis:
- malignant

6. APPROACH TO MORPHOLOGY
Architectural pattern:
1.Fasciculated spindle cell tumors
- Fibromatosis
- Cellular schwannoma
- Fibrosarcoma
- Leiomyosarcoma
- Spindle cell
rhabdomyosarcoma
- Synovial sarcoma
- Malignant peripheral
nerve sheath tumor
Leiomyosarcoma

7. DFSP
2. “Storiform”
Tumors(CARTWHEEL)
• Dermatofibrosarcoma protuberans
(DFSP)
• Other fibrohistiocytic tumors
• Occasional leiomyosarcomas
• Some malignant peripheral nerve
sheath tumor
• Malignant fibrous histiocytoma
• Occasional synovial sarcomas
• Solitary fibrous tumors
3.Herringbone Tumors
• Fibrosarcoma
• Synovial sarcoma
• Neurofibrosarcoma
• Solitary Fibrous Tumor
DFSP
)
DFS
P
Fibrosarcom
a)

8. 4.Palisading tumor
Schwannoma
Malignant peripheral nerve sheath
tumor
Leiomyosarcomas
Extragastrointestinal stromal tumor
Synovial sarcoma(rare)
5.Rosettes, pseudorosettes
Neuroblastoma
Neuroepithelioma
MPNST(rare)
Schwannoma
Neuroblastoma

9. 6.Alveolar pattern
• Alveolar RMS
• Alveolar soft part sarcoma
7.Biphasic pattern
• Synovial sarcoma
• Mesothelioma
Alveolar soft part sarcoma
Synovial sarcoma

10. 8.PLEXIFORM:
NEUROFIBROMA
9.Lobular:
•Lipoblastoma
•Liposarcoma
•Epithelioid sarcoma
•Clear cell sarcoma
8. Plexiform:
Neurofibroma

11. 10.Angiosarcoma
Anastomosing
ectatic vascular
channels that are
lined by highly
atypical endothelial
cells

12.  Degree and type of cellular
differentiation(Morphology specific
to tumor/lineage)
Lipoblasts – sharply defined
intracellular droplets of lipid and 1
or more centrally or peripherally
placed nuclei
 Rhabdomyoblasts – identified by
their deeply eosinophilic cytoplasm
with whorls of eosinophilic fibrillary
material near the nucleus and
cytoplasmic cross striations.

13. • Smooth muscle cells: Elongated shape,
eosinophilic longitudinal fibrils in
cytoplasm and cigar shaped nuclei
• Fibroblasts: Spindle in shape with
Elongated fusiform nuclei
• Nerve fibre: wavy shape with serpiginous
hyperchromatic nuclei (Wavy with pointed
end)

14. • Round cells in round cell sarcomas
–
Neuroblastoma
Extraskeletal Ewing’s sarcoma
Desmoplastic small round cell
tumor
Ewing’s sarcoma/ PNET
RMS

15. • Epithelioid Cells:
Alveolar soft part sarcoma
Epithelioid sarcoma
Epithelioid
hemangioendothelioma
Epithelioid Angiosarcoma
Epithelioid variant of MPNST
Epithelioid Schwannoma
Epitheliod sarcoma
Epithelioid
hemangioendothelioma
with cytoplasmic vacuoles
that “blister” the cell.

16. Pleomorphic tumors:
• Diagnoses relies on tumor
sampling to identify areas
of specific differentiation.
- Undifferentiated
pleomorphic sarcoma
-Pleomorphic
Liposarcoma
-Pleomorphic RMS
- Pleomorphic MPNST.
Pleomorphic RMS

17. OTHER FEATURES:
Distinguishing Fibroblasts, myofibroblasts, schwann cells,
and spindle cells of synovial sarcoma and mesothelioma is
often based on location and growth pattern- positive
identification often requires IHC and electron microscopic
analysis
Mitotic count – done on high power field, useful for
diagnosing benign v/s malignant; low grade v/s high grade
Nuclear atypia helpful for differentiating benign from
malignant
Hemorrhage & necrosis- more likely to be malignant

18. ROLE OF
IMMUNOHISTOCHEMISTRY
• Panels of immunostains should be used based on patterns
expressed in histopathology
• Initial IHC panel is used to rule out non mesenchymal tumor
followed by secondary panel for defining mesenchymal cell
lineage
• Extent of subcategorization should be on based on clinical
relevance
• Espescially helpful in tumors of uncertain cell lineage and
tumors with primitive small round cell morphology which are
often characterized by a unique immunohistochemical
phenotype

19. Broad categories of neoplasia
Carcinoma
PanCK, LMW
CK, HMWCK,
EMA
Sarcoma
Vimentin+
PANCK-
Lymphoma
LCA(CD45)
Germ cell tx
PLAP+ve
Melanoma
S100+
CD3,CD2
0,CD23,
CD43,
C30
MyoD1,
myogenin,
CD 31,CD 34,
S100, bcl2,
factor VIII
MelanA, HMB45
AFP,B-
HCG,
CD30,
CD117
Secondary
Panel
according
to
morpholog
y & Site

20. ROUTINE IHC MARKERS IN SOFT
TISSUE TUMOURS
DESMIN Sarcomas( smooth, skeletal muscle, endometrial
stromal)
CD31, CD34 Vascular tumours
S100 Sarcomas with neural, lipomatous , chondroid
differentiation
VIMENTIN Many sarcoma, nonspecific
CK, EMA, CD99, BCL2 Synovial sarcoma
CD117 Gastrointestinal stromal tumours
BETA-CATENIN DESMOID FIBROMATOSIS
CD99, S100, VIMENTIN PNET/EWING sarcoma
CK, CD99, DESMIN, NSE Desmoplastic small round cell tumours
S100 MPNST

21. APPROACH TO IHC MARKERS
• Lineage specific marker (Vimentin/CK/LCA)
• Further panel based on architecture and
cytomorphology

25. NOVEL IMMUNOHISTOCHEMICAL MARKERS IN
SOFT TISSUE TUMORS
 Over the last decade, much more specific immunohistochemical markers for
soft tissue tumours have been developed.
 These useful new diagnostic markers can be separated into three general
categories:
(1) Lineage-restricted transcription factors
(2) Protein correlates of molecular alterations
(3) Diagnostic markers identified by gene expression profiling.
 Antibodies are helpful and relatively specific diagnostic markers.

26. MYOGENIN, MYOD1 EXPRESSION IN
RHABDOMYOSARCOMAS
a) Alveolar RMS showing a solid growth pattern. b) strong nuclear staining in nearly all tumor
cells.
c) Embryonal RMS composed of round-short spindled cells in myxoid stroma d) Only a subset of
tumor cells is positive
 Myogenin & MyoD1 are
myogenic
transcriptional
regulatory proteins
expressed early in
skeletal muscle
differentiation.
 Considered sensitive and
specific markers for
RMS.

27. ERG & FLI1(ETS FAMILY TRANSCRIPTION FACTORS)
Expression of two related ETS family transcription factors is
relatively restricted to endothelial cells and derived neoplasms.
Most common translocation in Ewing sarcoma is t(11;22), found in
~90% of cases and it leads to EWSR1-FLI1 fusion and
overexpression of the FLI1 protein.
FLI1 is also expressed in endothelial cells and derived neoplasms,
lymphoblastic lymphomas, and occasionally in a wide range of
mesenchymal neoplasms.

28. (a)Poorly differentiated cutaneous angiosarcoma infiltrating dermal
collagen.
(b)ERG shows strong nuclear staining in tumor cells.
ERG(ETS-RELATED GENE IS A HIGHLY SENSITIVE AND SPECIFIC MARKER FOR
ENDOTHELIAL DIFFERENTIATION

29. Β-CATENIN STAINING IN
DESMOID FIBROMATOSIS
Desmoid fibromatosis composed of bland
myofibroblastic spindle cells arranged in long fascicles.
 β-Catenin is the product of the CTNNB1
gene involved in the Wnt signaling
pathway.
 Mutations in CTNNB1 are found in 85–
90% of sporadic desmoid tumors.
 Consistently negative in other intra-
abdominal mesenchymal neoplasms
(including GISTs and smooth muscle
tumors).
 Not entirely specific(Subset of solitary
fibrous tumors (20– 40%) and low-grade
myofibroblastic sarcomas (30%) also
show nuclear staining).

30.  Well differentiated liposarcoma and dedifferentiated liposarcoma are
characterized by supernumerary ring and giant marker chromosomes,
within which several oncogenes are located, leading to overexpression of
MDM2 and CDK4.
 First line tool for separating ALT/WDL from benign lipomatous lesion.
 Nuclear reactivity for MDM2 and CDK4 is highly sensitive, but is not
entirely specific.
 Indication for MDM2 gene analysis in lipomatous tumor- 1) lipomatous
tumor with equivocal cytological atypia 2)Recurrent lipoma 3)deep lipoma
without atypia, size >15cm 4)Retroperitoneal lipomatous tm lacking
cytological atypia.
 Combined positive staining for both MDM2 and CDK4 is much more
specific.
MDM2 AND CDK4 EXPRESSION

31. MDM2 AND CDK4 EXPRESSION IN LIPOSARCOMAS
Well-differentiated liposarcoma (MDM2) dedifferentiated liposarcoma(CDK4)Dedifferentiated liposarcoma
(MDM2)

32. NOVEL IMMUNOHISTOCHEMICAL MARKERS IN SOFT TISSUE TUMORS

34. TUMORS OF UNCERTAIN ORIGIN
1.Extraskeletal Ewing Sarcoma / PNET
2. Synovial sarcoma
3.Epitheloid sarcoma
4.Alveolar soft part Sarcoma
5. Desmoplastic Small round cell tumor
6.Clear cell sarcoma of soft tissue.

35. EXTRASKELETAL EWING SARCOMA
Ewing sarcoma shows membranous staining with CD99. A, Ewing sarcoma by
hematoxylin-eosin (original magnification 20). B, Membranous CD99 staining of
Ewing sarcoma (original magnification 40).
Highly aggressive primitive round cell tumor of uncertain histogenesis with
variable degrees of neural differentiation
Useful markers: CD99
FLI-1
Neural markers - S100, CD56, chromogranin, and synaptophysin may be positive
but are often only focally or weakly

36. SYNOVIAL
SARCOMA
• Unique soft tissue sarcoma showing
both mesenchymal and epithelial
differentiation
• Despite its name, it is neither related
to nor arising from synovial cells.
• Immunohistochemistry is
particularly useful in the diagnosis of
the monophasic spindle cell variant
Useful markers:
• EMA+ (95%)
• AE1/AE3+ (65%)
• S100 + (30%)
• CD99 + (>50%)
• CD34 (+ 5%) High-molecular-weight cytokeratin
immunoreactivity highlights the epithelial
elements in this biphasic synovial sarcoma.

37. EPITHELIOID SARCOMA
• Rare soft tissue sarcoma showing epithelial differentiation
• Useful markers : CK, EMA, CD34 +
CD31-
S100 and desmin are only rarely positive

38. DESMOPLASTIC SMALL ROUND TUMOR
• Composed of small round tumor cells of uncertain
histogenesis associated with prominent stromal
desmoplasia
• Polyphenotypic expressing epithelial, muscular and neural
markers
• simultaneously
• Majority of cases are positive for CK, EMA, vimentin,
desmin, NSE
• Myogenin and myoD1 are consistently negative

39. Photomicrograph of desmoplastic small
round cell tumor (hematoxylin-eosin,
original magnifications 10(a)and, showing
coexpression of cytokeratin (original
magnification 20 [c]) and desmin (original
magnification 20 [d]).

40. CLEAR CELL SARCOMA OF SOFT TISSUE
• Positive for melanocytic markers
S100, HMB-45, and less consistently
for melan (Mart-1)
• Other positive markers include
neuron-specific enolase, CD57 and
vimentin
• Distinction from cutaneous
melanoma is based on tumor
morphology, location, or genetic
confirmation
S10
0
HMB45

41. ALVEOLAR SOFT PART SARCOMA
• No consistent positive IHC
finding
• A unique feature of this sarcoma
is its weak or even negative
staining with vimentin.
• Periodic acid-Schiff (PAS) staining
with diastase reveals varying
amounts of intracellular
crystalline material
• S100 and desmin staining is
sometimes present, but the
expression of these markers have
no significance in the
histogenesis of this tumor
• A new immunohistochemical
stain for TFE3 protein has been
developed
Periodic acid-Schiff (PAS) stainings intracellular crystalline material

42. GRADING OF SARCOMAS
• Grading assesses the degree of malignancy of sarcoma and is based
on evaluation of several histologic parameters
• Central and necessary element of the major clinical staging systems
for sarcoma
• Main aim - better predicting prognosis and metastatic risk and
facilitating patient treatment.
• Ideally good prognosis group encompass tumors having a
propensity for local recurrence, have very low metastatic potential
and are amenable to surgical treatment alone.
• The tumors in the poor prognosis group should include sarcomas
likely to metastasize and for which adjuvant therapy might prove
beneficial
• The best established and most widely accepted grading schemes is
FNCLCC system (Fédération Nationale des Centres de Lutte Contre
le Cancer (also known as the French or “Trojani” system in France)

43. FNCLCC GRADING SYSTEM
• Tumour differentiation
Score 1: sarcomas closely resembling normal adult mesenchymal tissue
(e.g., low grade leiomyosarcoma)
Score 2: sarcomas for which histological typing is certain (e.g., myxoid
liposarcoma).
Score 3: embryonal and undifferentiated sarcomas, sarcomas of doubtful
type, synovial sarcomas, osteosarcomas, PNET.
• Mitotic count
Score 1: 0-9 mitoses per 10 HPF*
Score 2: 10-19 mitoses per 10 HPF
Score 3: *20 mitoses per 10 HPF
• Tumour necrosis
Score 0: no necrosis
Score 1: <50% tumour necrosis
Score 2: *50% tumour necrosis

44. • Grade 1: 2-3 score
• Grade 2: 4-5 score
• Grade 3: 6-8 score

45. ADIPOCYTIC TUMORS
• BENIGN
MALIGNANT
• Lipoma Atypical lipomatous
tumor
• Lipoblastoma Dedifferentiated
liposarcoma
• Angiolipoma Myxoid liposarcoma
• Myolipoma Pleomorphic
liposarcoma
• Hibernoma

46. LIPOMA
• Most common mesenchymal lesion in adults
• Subcutaneous/ deep soft tissues
• Painless soft mass
• Well circumscribed, yellow greasy cut surface

47. Lobules of mature adipocytes. Stain for S100, leptin and
HMGA2

48. LIPOBLASTOMA
• Benign neoplasm of embryonal white fat
• localized/diffuse
• 90% cases occur before age of 3 years
• Most commonly trunk/ extremities. May occur in
retroperitoneum, pelvis, abdomen, mesentery

49. Lobular architecture with fibrous
septa, lipoblasts in various stages of
differentiation

50. ATYPICAL LIPOMATOUS TUMOR
• Locally aggressive
• Deep soft tissues of limbs, followed by retroperitoneum
• Also known as well differentiated liposarcoma
• Presents as a deep seated, painless mass
• Large, well circumscribes, lobulated mass
• Morphologically: adipocytic, sclerosing and inflammatory
subtypes

51. • Relatively mature adipocytic proliferation
• Focal adipocytic nuclear atypia and hyperchromasia
• Scattered hyperchromatic and multinucleate stromal cells
may be seen
• Lipoblasts may be present
• Sclerosing type: scattered bizarre stromal cells, rare
multivacuolated lipoblasts, extensive fibrillary collagenous
stroma
• Inflammatory type: rare, chronic inflammatory infiltrate
may obscure the adipocytic component

53. Inflammatory subtype Sclerosing subtype

54. DEDIFFERENTIATED LIPOSARCOMA
• An atypical lipomatous tumor showing progression to
sarcoma of varying histological grade
• Retroperitoneum is most commonly involved
• Large multinodular yellow masses with tan grey areas
• These dedifferentiated areas show necrosis

55. • Histologic hallmark is transition from well differentiated to
non lipogenic sarcoma
• Usually abrupt transition
• Dedifferentiated areas most commonly resemble
undifferentiated pleomorphic sarcoma
• 5-10% cases may show heterologous
osteo/chondrosarcomatous differentiation
• IHC: Recognition of divergent differentiation. Diffuse
expression of MDM2 and/or CDK4

57. Myxoid Liposarcoma

58. FIBROBLASTIC TUMORS

59. FIBROMATOSIS
• Fibroblastic proliferations
• Local recurrence, do not metastasize
• Adults, increasing incidence with age
• Small nodules or ill defined conglomerate of nodular masses
• Cellular proliferation of plump , immature looking spindle cells,
little or no pleomorphism, normochromatic nuclei. Moderate
amount of stromal collagen and elongated blood vessels are
seen.
• IHC: SMA+
• 50% cases: nuclear immunopositivity for β catenin

60. FIBROMATOSIS

61. DERMATOFIBROSARCOMA
PROTUBERANS
• Superficial, low grade, locally aggressive
• COL1A1-PDGFB fusion gene
• Trunk and proximal extremities
• Present as nodular cutaneous mass
• Characterised by diffuse infiltration of dermis and subcutis
• Neoplastic cells grow along the fibrous septa of subcutaneous
tissue and interdigitate with fat lobules (HONEYCOMB)
• Cytologically uniform spindle cells, plump to elongated wavy
nuclei, storiform pattern. Minimal atypia, mitosis.

64. ADULT FIBROSARCOMA
• Malignant neoplasm c/o fibroblasts with variable collagen
production and “herringbone architecture”
• Deep soft tissues of extremities, trunk, head and neck
• Painless/painful masses
• Circumscribed, firm, white or tan mass
• Relatively monomorphic spindle cells, mild to moderate
pleomorphism
• Tumor cells arranged in long sweeping fascicles in
herringbone pattern
• Variable mitotic activity , collagenous stroma

65. FIBROSARCOMA

66. MYXOFIBROSARCOMA
• Malignant fibroblastic neoplasms
• Most common in elderly patients
• Most commonly in the limbs
• Multiple, variable gelatinous nodules on cut surface
• Broad spectrum of cellularity, pleomorphism
• Multinodular growth with incomplete fibrous septa and
myxoid stroma
• Prominent elongated, curvilinear, thin walled blood vessels
with perivascular condensation of tumor cells

67. MYXOFIBROSARCOMA

68. SMOOTH MUSCLE TUMORS
• Leiomyoma
• Leiomyosarcoma

69. LEIOMYOSARCOMA
• Malignant neoplasm showing pure smooth muscle
differentiation
• Middle aged/elderly
• Commoner in women
• Most common location is the retroperitoneum
• Fleshy, grey to tan mass, whorled cut surface
• Intersecting, sharply marginating fascicles of spindle cells
• Nuclei are classically elongated and blunt ended
• Fair number of mitosis, some atypical

70. • IHC:
• SMA, desmin, Caldesmon +
• Keratin, EMA, CD34 and S100 may be focally positive

71. PERICYTIC TUMORS
• Glomus tumor
• Myopericytoma
• Angioleiomyoma

72. GLOMUS TUMOR
• Mesenchymal neoplasms composed of cells resembling
modified smooth muscle cells of the glomus body
• Rare, <2% of soft tissue tumors
• Mostly in young adults
• Majority occur in distal extremities (subungual region)
• Typically small, red-blue nodules, painful, especially with
cold or tactile stimulation
• IHC: Typically express SMA and have abundant extracellular
production of type IV collagen

74. Small, rounded with centrally placed nucleus

75. SKELETAL MUSCLE TUMORS
• Rhabdomyoma
• Rhabdomyosarcoma

76. RHABDOMYOSARCOMA
• Malignant soft tissue sarcoma of skeletal muscle
• Subtypes: Alveolar, embryonal , pleomorphic
• Cell of origin: Rhabdomyoblast
• Most common STS of childhood
• IHC: Desmin, Myogenin,
MyoD1, Myoglobin

79. VASCULAR TUMORS
• Hemangiomas
• Angiomatosis
• Lymphangioma
• Kaposiform hemangioendothelioma
• Retiform hemangioendothelioma
• Kaposi sarcoma
• Epithelioid hemangioendothelioma
• Angiosarcoma

80. ANGIOSARCOMA
• Malignant
• All ages, peak in seventh decade
• Most commonly in deep muscles of lower
extremities>retroperitoneum>mediastinum
• Painful enlarging mass of several months duration
• Multinodular hemorrhagic masses with cystic degeneration
and necrosis
• IHC: CD34, CD31, ERG, FLI1, occasional podoplanin

81. • Areas of well formed anastomosing vessels to solid sheets
of high grade epithelioid or spindled cells (epithelioid
angiosarcomas)
• Multiple patterns may be observed
• Vasoformative areas: ramifying channels lined by atypical
endothelial cells

82. REFERENCES
• WHO Classification of Soft tissue and Bone 4th edition
• Weiss, S.W., Goldblum, J.R. (2007). Enzinger and Weiss’ soft
tissue tumors. St. Louis, Mo, Mosby.