My Approach to
Diagnosis of Soft Tissue Tumors
Savannah, GA
October 2019
Cyril Fisher MA MD DSc FRCPathConsultant Pathologist,
University Hospitals Birmingham, UK
Professor Emeritus of Tumor Pathology
Institute of Cancer Research
University of London, UK
Soft Tissue Sarcomas
• Rare: sarcomas 1% of all cancers
• 50 per million: Per annum 3600
• Can arise virtually anywhere
• skin, subcutis, deep soft tissue
• organs (i.e. non soft tissue sites)
• Seen in general surgical pathology practice
• >200 subtypes
• Can mimic carcinoma, melanoma, lymphoma
Classification
• By differentiation
• (WHO consensus
2002, 2013)
• Adipocytic
• Fibroblastic/myofibroblastic
• Fibrohistiocytic
• Smooth or skeletal muscle
• Pericytic (perivascular)
• Vascular
• Chondro-osseous
• Neural
• GIST
• Uncertain differentiation
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Liposarcoma
Dedifferentiated
ALT/Well differentiated Pleomorphic
Epithelioid pleomorphic
Myxoid
Myxoid
complex karyotypet(12;16)(q13;p11) FUS-DDIT3
t(12;22)(q13;q12) EWSR1-DDIT3
t(12;16)(q13;p11) FUS-DDIT3
t(12;22)(q13;q12) EWSR1-DDIT3complex karyotype
12q13-15 amplifications
12q13-15 amplifications & others
Uncertain Differentiation
Synovial sarcoma
epithelial
Epithelioid sarcoma
epithelial (part)
Clear cell sarcoma
melanocytic
Ewing sarcoma/PNET
neuroectodermal
Desmoplastic SRCT
?mesothelial
E/S myxoid chondrosarcoma
?
Alveolar soft part sarcoma
?
PEComa
myomelanocytic
Gastrointestinal stromal tumor
?interstitial cell of Cajal
Classification
• By behavior
• (WHO consensus
2002, 2013)
• Benign
• Intermediate
• locally aggressive
• rarely metastasising
• Malignant – sarcoma
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Common Benign Soft Tissue Tumors
Common Benign ST Tumors
• Lipoma
• Myxoma
• Schwannoma
• Leiomyoma
• Hemangioma
• Nodular fasciitis
Locally aggressive
• Atypical lipomatous tumor
• Fibromatosis
• Lipofibromatosis
• Giant cell fibroblastoma
• Kaposiform HE
• Haemosiderotic fibrolipomatous tumor
Intermediate ST Tumors
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Fibromatosis
Fibromatosis
Beta catenin
Dermatofibrosarcoma
Inflammatory myofibroblastic t.
Low grade myofibrosarcoma
Solitary fibrous tumor
Myxoinflammatory fibroblastic
sarcoma
Infantile fibrosarcoma
Plexiform fibrohistiocytic tumor
Giant cell tumor of soft tissue
Intermediate ST Tumors
Hemangioendothelioma
retiform, composite,
papillary, pseudomyogenic
Kaposi sarcoma
Atypical fibroxanthoma
Angiomatoid fibrous histiocytoma
Ossifying fibromyxoid tumor
Myoepithelial tumors
Phosphaturic mesenchymal tumor
Rarely metastasizing <2%
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Sarcomas
• grade 1
• grade 2
• grade 3
Malignant ST Tumors
Soft Tissue Tumor Diagnosis
• Identify differentiation (‘lineage’)
• not from corresponding mature tissue
• cannot define cell of origin (‘histogenesis’)
• Assess malignant potential
• Clinicopathological perspective
➔ predict behavior
➔ guide treatment
➔ assess progress
Approach to Diagnosis
• Clinical features
• Gross findings
• Histology
• Ancillary techniques
• immunohistochemistry
• molecular genetics
• electron microscopy
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STT – Clinical Information
Past Medical History
• Trauma/surgery
• Previous disease
• Previous therapy
• immunosuppression
• lymphoedema
• therapeutic irradiation
Family history
• Cancer predisposition
syndromes
Mass
• Painless
• Painful
Mass effect
• Paraesthesia
• Thrombus
• Obstruction
STT – Clinical Features
• Age
• Sex
• Site
• Duration
• Size
• Depth
• Diagnostic spectrum of
malignancies is different in children
• Different tumor types occur in➔
different age groups in adults
Clinical Features - Age
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Childhood
• Neuroblastoma
• Embryonal RMS
• Acute lymphoblastic
leukaemia
• Wilms tumor
Clinical Features - Age
Adolescent
• Alveolar RMS
• Ewing sarcoma
• Desmoplastic SRCT
• Poorly differentiated
synovial sa
• Mesenchymal chondrosa
• ALL
Clinical Features - Age
Adult
• Small cell carcinoma
• Small cell melanoma
• Small cell lymphoma/leuk.
• Alveolar RMS
• Ewing sarcoma
• Round cell liposarcoma
• Poorly differentiated
synovial sa
• Endometrial stromal sa
Clinical Features - Age
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Site
Depth from surface
• Most benign tumors
occur superficially
• Site and depth relate
to prognosis
• Staging
Clinical Features
Clinical Features
Site
Depth from surface
• Most benign tumors
occur superficially
• Site and depth relate
to prognosis
• Staging
Clinical Features
Site
Depth from surface
• Most benign tumors
occur superficially
• Site and depth relate
to prognosis
• Staging
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Duration and Size
• Sarcoma ➔ longer history, larger
• Nodular fasciitis ➔ rapid growth (self-limiting)
Clinical Features
• Small specimens
• FNAC
• core needle biopsies
• open biopsies
• some resections
• Large specimens
• resections
• amputations
Types of Specimen
Core biopsies
• Embed one core per
cassette
• No levels
➔ maximal use of
available tissue
Lesions <5cm
• Embed in entirety
Small Specimens
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• Weigh, measure (mms)
• Ink margin(s)
• Fresh tissue ➔ freeze
Larger Specimens
Gross description
• Solid, cystic
• Myxoid, fibrous
• Estimate necrosis
• Dedifferentiation
Sample
• 1 block/cm
• Margins
• nearest
Larger Specimens
Intra-abdominal
mass
2019
Review Previous Pathology
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Intra-abdominal
mass
2012
Review Previous Pathology
Tissue plane
• Skin/subcutis/fascia/
muscle
Margin
• Circumscribed, infiltrative
Cellularity
• Sparse/moderate/high
Stroma
• collagenous
• hyalinised
• myxoid
• Inflammatory
Low Magnification
Some tumors resemble
corresponding normal
tissue
Morphology
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Some tumors resemble
corresponding normal
tissue
Morphology
Spindle cell
Small round cell Pleomorphic
Epithelioid
Morphology
Low power:
Patterns
• Sheets
• Nests
• Files
• Fascicles
• intersecting
• sweeping
• alternating
• storiform
• herringbone
• palisading
• Myxoid
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Fibroblasts Myofibroblasts
Smooth muscle Nerve sheath
Synovial sarcoma ‘Fibrohistiocytic’
Benign or Malignant?
• Synthesis of factors
• Pleomorphism
• Atypical mitoses
• Necrosis
• But vary according to lineage!
Symplastic LeiomyomaAtypical Schwannoma
PHAT Atypical Cutaneous FH
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• In complex karyotypic
tumors
• Not in translocation-
associated sarcomas
Pleomorphism/Atypia
LGFMS
SSES
Benign/reactive
• <5/10hpf
• (normal)
• nodular fasciitis
Malignant
• >5/10hpf
• abnormal forms
Mitoses
Per 10 hpf
• Grading criterion
Per 50 hpf
• GIST
• Ossifying fibromyxoid t.
• Glomus tumor
• Deep leiomyoma
Mitotic Index
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Immunohistochemistry
Soft Tissue Tumor Immuno Panels
Spindle
CK
CD34
SMA
Desmin
S100 pr
SOX10
MUC4
STAT6
Small round
CK
Desmin
Myogenin
CD99
FLI-1
WT1
S100 pr
NB84a
NF/NSE
CD45
Tdt
Pleomorphic
CK
SMA
Desmin
S100 pr
CDK4
p16
MDM2
Epithelioid
CK
EMA
CD34
CD31
ERG
SMA
Desmin
S100 PgR
SOX10
HMB45
Melan-A
INI1
‘Specific’ Abs According to Context
• Beta-catenin Fibromatosis
• ALK, ROS1 Inflammatory myofibroblastic tumor
• p16, MDM2 & CDK4 WD/DD liposarcoma
• INI1 Epithelioid sarcoma et al
• STAT6 Solitary fibrous tumor
• MUC4 LG fibromyxoid sarcoma
• SOX10, H3K27me3 MPNST
• CD117, DOG1 GIST
• MYC Angiosarcoma
• FOSB Epithelioid hemangioma
• RB Spindle cell lipoma
• Brachury Chordoma
• NKX2.2 Ewing sarcoma
• ETV4 CIC-DUX4 sarcoma
• CCNB3 CCNB3-BCOR sarcoma
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Immunohistochemistry
• Know purpose of each antibody
• Never rely on a single marker
No marker is 100% sensitive or specific
• Use selected panels
• Specific cellular compartment
• Negative as well as positive finding
Cytokeratin
• Widespread
• carcinoma (organ-
based)
• some sarcomas
• Focal
• synovial sarcoma
Distribution of Immunoreactivity
Beta-Catenin
Positive Negative
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CD34 and Cytokeratin
• Epithelioid sarcoma
• Epithelioid endothelial tumors
• Ectopic hamartomatous thymoma
• Superficial CD34-positive fibroblastic tumor
• SMARCA4-inactivated undiff. thoracic tumor
• Desmoplastic nested spindle cell tumor
• Hepatocellular carcinoma
• NUT midline carcinoma
Useful negatives
• INI1 many
• H3K27Me3 MPNST
• STAT6 not SFT
• TLE1 not synovial sarcoma
• MUC4 not low-grade fibromyxoid sa
Natural History of a New Diagnostic Ab
Highly specific and sensitive for one tumor type
Occasionally positive in similar tumor types
Often positive in different tumor types
Used only as part of a larger panel of Abs
No longer used
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Molecular Diagnostics
• Make or confirm a
diagnosis
• Predictive /
prognostic factors
• Targeted therapy
When to do Molecular Testing
Molecular Abnormalities in STT
• Translocations
• Non-translocational abnormalities
• Somatic mutations• activating – KIT, PDGFRA
• non-activating – SMARCB1, TSC
• Copy number abnormalities
• gene amplification – MDM2
• gene deletion – SDH, SMARCB1, SMARCA4
• Complex unbalanced karyotypes
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Translocation-associated STT
Translocation-associated Sarcomas
• >30% of sarcomas
• Balanced or unbalanced
• non-pleomorphic but mostly G3
• Non-random, leads to new fusion gene
• transcriptional regulators
• tyrosine kinases
• growth factors
Malignant Soft Tissue Tumors
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Malignant Soft Tissue Tumors
Benign Soft Tissue Tumors
Genetics and Morphology
• Different genetic abnormalities can occur in tumors of
the same lineage or morphology
• Fibrosarcoma
• Myofibroblastic tumors
• Small round cell tumors
• Liposarcoma
• The same genetic abnormalities can occur in
completely different tumor types
• EWSR1 gene rearrangements
• ASPCR1-TFE3
• ETV6-NTRK3
• YWHAE-NUT22
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Fluorescence in situ
hybridization (FISH)
• gene rearrangements
• amplification
Reverse transcription
polymerase chain reaction
(RT-PCR)
• specific fusion transcripts
• mutational analysis
Molecular Diagnostic Techniques
FISH
Gene rearrangement Gene amplification
Caveats
FISH break apart
• sensitive but not
specific
Genes can partner
with multiple others
EWSR1
FUS
USP6 etc
FISH Diagnosis
USP6 in nodular fasciitis
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STT with EWSR1 Rearrangement
• EWSR1-FLI1, EWSR1-ERG,
EWSR1-many others
• Ewing & similar sarcomas
• EWSR1-WT1
• desmoplastic SRCT
• low grade myoid tumor
• EWSR1-DDIT3
• myxoid liposarcoma
• EWSR1-NR4A3
• e/s myxoid chondrosa
• EWSR1-CREB3L1
• sclerosing epithelioid fibrosa
• EWSR1-TFCP2
• rhabdomyosarcoma
• EWSR1-CREB1, EWSR1-ATF1
• various
• EWSR1-CREM
• myxoid mesenchymal tumor
hyalinising clear cell ca
• EWSR1-POU5F1,EWSR1-PBX1,
EWSR1-PBX3, EWSR1-ZNF44,
EWSR1-KLF17
• myoepithelial tumors
• EWSR1-YY1
• mesothelioma
• EWSR1-SMAD3
• acral spindle cell tumor
Thway 2012; Flucke 2012; Panagopoulos 2013; Gru 2013; Bilodeau 2013; Ud Din 2015; Huang 2015; Antonescu 2017; Kao 2018; Chapman 2018; Watson 2018
(Ewing sarcoma RNA-binding protein 1, 22q12.2)
Caveats
RT-PCR
• specific but cannot detect
uncommon fusions
• problems with RNA
extraction
• ‘promiscuity’ of fusions
Molecular Diagnosis
‘Promiscuous’ Fusions• EWSR1-ATF1
angiomatoid FH, clear cell sarcoma, CCSLTGITmyoepithelial tumor, angiosarcoma, salivary HCCC, CCOC
• EWSR1-CREB1angiomatoid FH, clear cell sarcoma, CCSLTGIT, PPMS
• EWSR1-CREMangiomatoid FH, intracranial myxoid mesenchymal tumor, CCS
• ETV6-NTRK3infantile fibrosarcoma, inflammatory myofibroblastic tumor, mesoblastic nephroma, AML, secretory ca breast,mammary analogue secretory carcinoma of salivary glands
• ASPSCR1-TFE3alveolar soft part sa, juvenile renal cell carcinoma
• TMP3-ALKinflammatory myofibroblastic tumor, anaplastic large cell lymphoma
• YWHAE-NUTM22A/Bendometrial stromal sarcoma, clear cell sarcoma of kidney
• FUS-ERGEwing sarcoma, AML
• BRD4-NUTEwing-like sarcoma, thymic & other carcinomas
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• Always interpret molecular findings in context of
• morphology
• clinical features
Molecular Diagnosis
Additional Approaches
• Gene expression profiling
• new antibodies
• predict behavior
• Comparative genomic hybridization
• copy numbers
• Epigenetics
• DNA methylation, miRNAs, sRNAs
• Protein expression profiling
Next Generation Sequencing
• Identifies molecular events
• Targetable mutations
• single-nucleotide variants,
• small insertions & deletions
• copy number variation
• complex structural variations
• Fusion genes
• Gene Signatures
Jour 2014; van de Rijn 2014
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CINSARC
• Complexity INdex in SARComas
• Gene expression signature (67 genes)
• Frozen tissue in microarray
• NGS - RNA sequencing in paraffin
• Can predict metastasis in
• leiomyosarcoma, UPS, DDL
• synovial sarcoma
• CDCA2 or KLF14
– Small molecule inhibitors
Chibon 2010; Lagarde 2013; Lesluyes 2016
Predicting Behavior - Prognostic Factors
• Age
• Site
• Size
• Grade
• Stage
• Proliferation markers
• Differentiation markers
French Cancer Centers Grading System
• Differentiation score- resembles normal- definite type- pleomorphic or undifferentiated
• Mitotic count (/10hpf)0-9, 10-19, 20+
• Necrosis0, <50%, >50%
• GRADE:2,3 = G1; 4,5 = G2; 6,7,8 = G3
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Caveats
Tumors which are intrinsically
high grade
Rhabdomyosarcoma
Ewing sarcoma / PNET
Soft tissue osteosarcoma
Mesenchymal chondrosarcoma
Epithelioid sarcoma
Clear cell sarcoma
Grade does not always
correlate with
outcome/behavior
Angiosarcoma
MPNST
Grading
Take home messages
• Clinical context
• Methodical approach
• Not everything in soft tissue is mesenchymal
THE END
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