Recent advances in soft tissue tumors

AZFAR NEYAZ, JUNIOR RESIDENT

SGPGIMS, LUCKNOW

• Soft tissue tumours represent a heterogeneous group of mesenchymal lesions

• Substantial developments in immunohistochemistry, cytogenetics & molecular genetics have caused a significant change in the classification and diagnosis

• In 2002, for the first time extensive genetic data were incorporated in WHO classification

• Concepts of so-called ‘malignant fibrous histiocytoma’ and ‘haemangiopericytoma’ began to be dismantled

Evolving classification of soft tissue tumours

• The new WHO classification of soft tissue tumours was published in 2013

• The changes in the 2013 classification are somewhat less dramatic than 2002

• There have been substantial steps forward in molecular genetic and cytogenetic characterization of this family of tumours

• The new classification also now incorporates gastrointestinal stromal tumours and peripheral nerve sheath tumours.

• WHO felt that these groups of lesions fitted better under the heading of ‘Soft tissue tumours’

Evolving classification of soft tissue tumours

WHO working group divides soft tissue tumors into four categories:

• Benign: do not recur locally and almost always cured by complete local excision

• Intermediate(locally aggressive): Recur locally and are associated with an infiltrative locally destructive growth pattern

• Intermediate (rarely metastasizing): often locally aggressive & show well documented ability to give rise to distant metastasis. The risk of such metastasis is <2%

• Malignant: have significant risk of distant metastasis (ranging from 20% to almost 100% depending upon histological type and grade

Staging and Grading

• Unlike with other tumors the staging of soft tissue tumors is largely determined by grade

• There is no generally agreed upon scheme for grading soft tissue tumors

• Most widely used grading systems are French Federation of Cancer Centers Sarcoma Group (FNCLCC) and National Cancer Institute (NCI)

• Both has 3 grades and are based on mitotic activity, necrosis and differentiation which correlate well with the prognosis.

• In addition to these criteria, NCI system requires the quantification of cellularity and pleomorphism for certain subtypes of sarcomas

FNCLCC grading system

• The TNM staging system recommends the FNCLCC system

• Grading of MPNST, embryonal and alveolar RMS, angiosarcoma, myxoidchondrosarcoma, alveolar soft part sarcoma, clear cell sarcoma, and epithelioid sarcoma is not recommended

WHO classification of soft tissue tumours (2013)

• ADIPOCYTIC TUMOURS

• FIBROBLASTIC / MYOFIBROBLASTIC TUMOURS

• FIBROHISTIOCYTIC TUMOURS

• SMOOTH MUSCLE TUMOURS

• PERICYTIC (PERIVASCULAR) TUMOURS

• SKELETAL MUSCLE TUMOURS

• VASCULAR TUMOURS

• GASTROINTESTINAL STROMAL TUMOURS

• NERVE SHEATH TUMOURS

• CHONDRO-OSSEOUS TUMOURS

• TUMOURS OF UNCERTAIN DIFFERENTIATION

• UNDIFFERENTIATED/UNCLASSIFIED SARCOMAS

ADIPOCYTIC TUMOURS

Benign

• Lipoma

• Lipomatosis

• Lipomatosis of nerve

• Lipoblastoma/Lipoblastomatosis

• Angiolipoma

• Myolipoma

• Chondroid lipoma

• Spindle cell/Pleomorphic lipoma

• Hibernoma

Intermediate (locally aggressive)Atypical lipomatous tumour/ Well differentiated liposarcoma

MalignantDedifferentiated liposarcomaMyxoid liposarcomaPleomorphic liposarcomaLiposarcoma-NOS

˟

• Term small cell liposarcoma is deleted

• It simply represent histological continuum of high grade myxoid liposarcoma

• This concept is supported by the presence of same genetic abnormalities, most commonly t(12;16), which fuses the DDIT3 (CHOP) gene on 12q13 with the FUS (TLS) gene on 16p11

• The other minor change was deletion of the category of ‘mixed-type liposarcoma

• Represent unusual morphological patterns of de-differentiated liposarcoma.

FIBROBLASTIC / MYOFIBROBLASTIC TUMOURS

Benign

• Nodular fasciitis

• Proliferative fasciitis

• Proliferative myositis

• Myositis ossificans

• Ischaemic fasciitis

• Elastofibroma

• fibro-osseous pseudotumour of digits

• Fibrous hamartoma of infancy

• Myofibroma / Myofibromatosis

• Fibromatosis colli

• Juvenile hyaline fibromatosis

• Inclusion body fibromatosis

• Fibroma of tendon sheath

• Desmoplastic fibroblastoma

• Mammary-type myofibroblastoma

Intermediate (locally aggressive)

• Superficial fibromatoses (palmar / plantar)

• Desmoid-type fibromatoses

• Lipofibromatosis

Intermediate (rarely metastasizing)

• Solitary fibrous tumour

• Inflammatory myofibroblastic tumour

• Low grade myofibroblastic sarcoma

• Myxoinflammatory fibroblastic sarcoma

• Infantile fibrosarcoma• Giant cell fibroblastoma • Dermatofibrosarcoma protuberans (DFSP)

Malignant

• Adult fibrosarcoma

• Myxofibrosarcoma

• Low grade fibromyxoid sarcoma

• hyalinizing spindle cell tumour

• Sclerosing epithelioid fibrosarcoma

• Calcifying aponeurotic fibroma

• Angiomyofibroblastoma

• Cellular angiofibroma

• Nuchal-type fibroma

• Gardner fibroma

• Calcifying fibrous tumour

• Giant cell angiofibroma

• Nodular fasciitis, proliferative fasciitis and proliferative myositis, are in fact neoplastic

• Earlier, their nosological status was uncertain,

• These lesions have been found to have a consistent gene fusion, MYH9–USP6, indicating that they are clonal neoplasms

• USP6 fusion genes have been identified in structurally related aneurysmal bone cyst

• Another major change is inclusion of the closely related entities giant cell fibroblastoma and dermatofibrosarcoma protuberans (DFSP)

• Giant cell fibroblastoma was included in the intermediate (locally aggressive) category and DFSP was included in the rarely metastasizing category

FIBROBLASTIC / MYOFIBROBLASTIC TUMOURS

• DFSP are characterized by the presence of supernumerary ring chromosomes.

• These ring chromosomes were shown to contain an ‘occult’ translocation t(17;22) resulting in fusion of the COL1A1 and PDGFB genes

• There is a close relationship between low-grade fibromyxoid sarcoma (LGFMS) and sclerosing epithelioid fibrosarcoma (SEF)

• Genetically, subsets of SEF, show identical findings as in LGFMS like t(7;16)(FUS–CREB3L2/L1)

• It is unclear whether FUS and EWSR1-negative SEF represent an entity distinct from LGFMS, or a form of morphological progression

FIBROBLASTIC / MYOFIBROBLASTIC TUMOURS

SO-CALLED FIBROHISTIOCYTIC TUMOURS

Benign

• Giant cell tumour of tendon sheath

• Diffuse-type giant cell tumour

• Deep benign fibrous histiocytoma

Intermediate (rarely metastasizing)

• Plexiform fibrohistiocytic tumour

• Giant cell tumour of soft tissues

Malignant

• Pleomorphic ‘MFH’ / Undifferentiated pleomorphic sarcoma

• Giant cell ‘MFH’ / Undifferentiated pleomorphic sarcoma with giant cells

• Inflammatory ‘MFH’ / Undifferentiated pleomorphic sarcoma with prominent inflammation˟

• The major but not unexpected change here has been the final removal of the term‘malignant fibrous histiocytoma’(MFH)

• MFH was initially regarded as a true histiocytic neoplasm, showing facultative fibroblasticdifferentiation.

• Existence of MFH as a discrete entity (rather than a final common pathway for a varietyof poorly differentiated sarcomas) was itself challenged in a number of studies

• So-called ‘malignant fibrous histiocytoma’, now classified as ‘undifferentiatedpleomorphic sarcoma

FIBROHISTIOCYTIC TUMOURS

SMOOTH MUSCLE TUMOURS

• No major changes in this category

• Angioleiomyoma (vascular leiomyoma) was reallocated to the category of pericytic(perivascular) tumours

• Deep leiomyoma • Genital leiomyoma• Leiomyosarcoma

PERICYTIC (PERIVASCULAR) TUMOURS• Glomus tumour

• Myopericytoma

• Angioleiomyomas

• In the 2002 classification, the group of myopericytomas had been incorporated under this heading for the first time

• It is now acknowledged that myofibroma/myofibromatosis also represent the spectrum of myopericytic neoplasms

• It show predominantly myofibroblastic-like cytomorphology and prominent stromal hyalinization

• Angioleiomyomas (vascular leiomyomas) were placed in this category and they form a morphological continuum with the myoid end of the spectrum of myopericytomas

SKELETAL MUSCLE TUMOURS

Benign

• Rhabdomyoma

Malignant

• Embryonal rhabdomyosarcoma

• Alveolar rhabdomyosarcoma

• Pleomorphic rhabdomyosarcoma

• Spindle cell RMS

• Sclerosing RMS

SKELETAL MUSCLE TUMOURS• Spindle cell rhabdomyosarcoma had been regarded previously as a variant of embryonal

RMS, based on its generally good prognosis

• Spindle cell RMS is related very closely to sclerosing RMS, neither of these lesions is truly related to embryonal rhabdomyosarcoma

• Neither spindle cell nor sclerosing RMS shows any genetic overlap with either embryonal or alveolar rhabdomyosarcoma

• Recently rearrangements of the NCOA2 gene have been identified in infantile cases of spindle cell rhabdomyosarcoma

• Sclerosing cell RMS appear to be less chemosensitive than other RMS, the prognosis is worse in adults than in children.

Vascular tumors

Benign

• Haemangiomas of subcut/deep soft tissue:

• capillary

• cavernous

• arteriovenous

• venous

• intramuscular

• synovial

• Epithelioid haemangioma

• Angiomatosis

• Lymphangioma

Intermediate (locally aggressive)

• Kaposiform haemangioendothelioma

Intermediate (rarely metastasizing)

• Retiform haemangioendothelioma

• Papillary intralymphatic angioendothelioma

• Composite haemangioendothelioma

• Pseudomyogenic haemangioendothelioma

• Kaposi sarcoma

Malignant

• Epithelioid haemangioendothelioma

• Angiosarcoma of soft tissue

Vascular tumors

• Introduction of a new entity pseudomyogenic haemangioendothelioma

• Also known as epithelioid sarcoma-like haemangioendothelioma

• Very distinctive tumour, arising in the extremities of adolescents, young adults and multicentric in more than 50% of patients.

• They have a remarkably pseudomyogenic morphological appearance which would not suggest endothelial differentiation at first

• Immunohistochemistry and electron microscopy support their vascular nature

• These tumours also harbour a distinctive t(7;19)(q22;q13) chromosomal translocation.

GASTROINTESTINAL STROMAL TUMOURS

• Approximately 80% of GISTs harbour oncogenic mutations in KIT, and 8–10% harbouroncogenic mutations in PDGFRA,

• A new group of GISTs as been recognized in recent years, being characterized by loss offunction of the succinate dehydrogenase (SDH) complex

• These SDH-deficient GISTs, lack mutations in either KIT or PDGFRA

• Account for the important subset of tumours known as paediatric-type GIST

• Arise exclusively in the stomach, they can be multifocal, clinically very indolent

• The mechanism of SDH deficiency seems likely to be epigenetic (perhaps related tomethylation status). Only a small subset harbour a mutation in one of the SDH genes

Benign

• Schwannoma (including variants)

• Melanotic schwannoma

• Neurofibroma (including variants)

• Perineurioma

• Granular cell tumour

• Dermal nerve sheath myxoma

• Solitary circumscribed neuroma

• Ectopic meningioma

• Nasal glial heterotopia

• Benign Triton tumour

• Hybrid nerve sheath tumours

NERVE SHEATH TUMOURS

Malignant

• Malignant peripheral nerve sheath tumour

• Malignant granular cell tumour

• Ectomesenchymoma

NERVE SHEATH TUMOURS

• The current WHO classification included tumours previously classified under cranial and peripheral nerves, head and neck and skin tumours

• This represents an important initiative to present the diverse family of mesenchymal tumors into a single reference source

• One distinct group of newly recognized tumours included in the category of benign nerve sheath tumours were hybrid nerve sheath tumours

• By far the most common among which is hybrid schwannoma/perineurioma

• However, rare examples of hybrid neurofibroma/schwannoma are also recognized

TUMOURS OF UNCERTAIN DIFFERENTIATIONBenign

• Acral fibromyxoma

• Intramuscular myxoma (incl. cellular variant)

• Juxta-articular myxoma

• Deep (‘aggressive’) angiomyxoma

• Pleomorphic hyalinising angiectatic tumour

• Ectopic hamartomatous thymoma

Intermediate (locally aggressive)

• Haemosiderotic fibrolipomatous tumour

Intermediate (rarely metastasizing)

• Atypical fibroxanthoma

• Angiomatoid fibrous histiocytoma

• Ossifying fibromyxoid tumour (incl. atypical / malignant)

• Mixed tumour/Myoepithelioma/Parachordoma

• Phosphaturic mesenchymal tumour

Malignant• Synovial sarcoma • Epithelioid sarcoma• Alveolar soft part sarcoma • Clear cell sarcoma of soft tissue • Extraskeletal myxoid chondrosarcoma ("chordoid"

type)• Extraskeletal Ewing tumour • Desmoplastic small round cell tumour • Extra-renal rhabdoid tumour• Malignant mesenchymoma• Neoplasms with perivascular epithelioid cell

differentiation (PEComa)• Intimal sarcoma

TUMOURS OF UNCERTAIN DIFFERENTIATION

• Principal changes have been the addition of several recently recognized ‘entities

• In the benign category, acral fibromyxoma and atypical fibroxanthoma are now included

• Added into the intermediate (locally aggressive) category is haemosideroticfibrolipomatous tumour

• Haemosiderotic fibrolipomatous tumour have been shown to harbour the chromosome translocation t(1;10)(p22;q24)

• A new addition in the intermediate (rarely metastasizing) category is phosphaturicmesenchymal tumour,

• A tumour type which has been recognized for many years but which had not been defined clearly until more recently

• PNET has been dropped as a synonym for Ewing sarcoma in order to minimize confusion

• Malignant mesenchymoma is not included in the current classification.

• Most cases reported previously probably represent heterologous line of differentiation in specific sarcomas

TUMOURS OF UNCERTAIN DIFFERENTIATION

• Undifferentiated spindle cell sarcoma

• Undifferentiated pleomorphic sarcoma

• Undifferentiated round cell sarcoma

• Undifferentiated epithelioid sarcoma

• Undifferentiated sarcoma NOS

UNDIFFERENTIATED/UNCLASSIFIED SARCOMAS

UNDIFFERENTIATED/UNCLASSIFIED SARCOMAS• A subset of sarcomas cannot be classified into any presently defined categories and

account for up to 20% of all sarcomas

• A significant subset of radiation-associated sarcomas fall into this category.

• These lesions show no definable line of differentiation

• In round cell category, genetic subsets which almost certainly represent discrete entities are already beginning to be recognized,

• Most notably those characterized by CIC–DUX4 gene fusion, due to t(4;19) or t(10;19)

• It remains to be seen whether these cases represent one or more separate entities, or whether they are better classified as variants of Ewing sarcoma.

Immunohistochemistry in the diagnosis of soft tissue tumors

• Immunohistochemistry is an integral component in the proper analysis of soft tissue tumours

• The diagnostic approach consists in ruling out a non-mesenchymal tumor followed by trying to define mesenchymal cell lineage.

• It is best used as a diagnostic adjunct following careful assessment of histopathology and formulation of differential diagnosis

• The effective use of immunohistochemistry specifically assesses the differential diagnostic possibilities

Basic panel of antibodies

• Cytokeratin

• EMA

• S100

• Desmin

• SMA

• Vimentin

• CD 34• CD 31• CD 99• Bcl 2• LCA

• An initial panel of antibodies is often required in order to establish the broad lineage

• The initial battery of IHC markers should always include:

Cytokeratin• Collection of more than 20 proteins.

• Grouped by their mol. wt. into acidic and basic subfamilies.

• Their expression is not restricted to carcinomas.

Cytokeratin expression in soft tissue tumors

• Aberrenat CK expression can be found in many other sarcomas

• Significant percentage of smooth muscle and vascular tumors show CK positivity

EPITHELIAL MEMBRANE ANTIGEN( EMA)

• It is expressed in a variety of ductal, secretory and other epithelial cells

• EMA is also expressed in meningothelial and perineurial cell membranes

• EMA is useful in detecting epithelial differentiation in soft tissue tumours

• It is typically detectable in synovial sarcoma, epithelioid sarcoma, myoepitheliomaand many metastatic carcinomas

• Some other sarcomas, such as leiomyosarcoma, MPNST and rarely angiosarcomas, can also be positive, and this has to be considered in the differential diagnosis.

SMOOTH MUSCLE ACTIN(SMA)• SMA has specificity for smooth muscle cells. It is also expressed in the pericytes,

glomus cells, myofibroblasts and myoepithelial cells.

DESMIN• Desmin is useful in the diagnosis of skeletal muscle and smooth muscle tumours

• Desmin can also be present in myofibroblasts, therefore myofibroblastic tumours such as desmoid fibromatosis can be focally positive

• Desmin is expressed strongly in many other tumours, most important examples include desmoplastic small round cell tumour, which show perinuclear dots like positivity

• Ewing sarcoma occasionally show desmin positivity

• Belongs to family of calcium binding proteins

• Expressed in Glia, Schwann cells, Melanocytes, histiocytes, Chondrocytes, lipocytes, muscle, myoepithelial cells

• Diagnostic value in melanomas, peripheral nerve sheath tumors

• MPNST- only patchy and weak

• Other tumors expressing it-

• Malignant melanoma

• Synovial Sarcoma

• RMS

• LMS

• Adipocytic tumors

• Chondrocytic tumors

• Myoepithelioma

S-100 protein

Applications for CD34 shown by pairs of tumors with potential histological resemblance

CD 34

CD99• Uniformly express CD99 with a characteristic membranous pattern in Ewing sarcoma

• But it is not so specific

• Positivity is seen in lymphomas, RMS, Mesothelioma, synovial sarcoma, solitary fibrous tumor, desmoplastic small round cell tumor etc.

Bcl-2• It is a family of protein involved in the apoptosis pathway in cell grown and death• Positive in Solitary fibrous tumor, Synovial sarcoma, DFSP

• CD31 has been the gold standard as a marker for endothelial differentiation

• Diagnosis of malignant vascular tumours like epithelioid haemangioendothelioma, angiosarcomas and Kaposi sarcoma is aided by demonstration of CD31

CD 31

Novel immunohistochemical markers in soft tissue tumors

• Until recently, the primary purpose of immunohistochemistry was simply to attempt to

demonstrate a line of differentiation

• Most traditional markers show relatively limited specificity

• Over the last decade, much more specific immunohistochemical markers for soft tissue tumors have been developed

• These useful new diagnostic markers can 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

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

ERG & FLI1(ETS family transcription factors)

• Expression of two related ETS family transcription factors is relatively restricted to endothelial cells and derived neoplasms

• The 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

• Given its lack of specificity, FLI1 immunohistochemistry is not particularly helpful in differential diagnosis

(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

Brachyury• It is a transcriptional activator involved in the development of the notochord

• Nuclear expression of brachyury is a consistent feature of chordoma

• Helpful in distinguishing chordoma from chondrosarcoma, metastatic carcinoma and myoepithelial tumors

Epithelioid cells with abundant eosinophilic cytoplasm, cytoplasmic vacuoles, and scant myxoid stroma.

SOX10 (SRY-related HMG-box 10) expression

a) Neurofibroma with buckled nuclei and prominent collagenous stroma b) SOX10- positive in the Schwann cell

c) MPNST with fascicular architecture, tapering nuclei & high mitotic rate d) Nucleopositivity is + in a small no of cells.

• Important for embryonicdevelopment and cell fate determination of the neural crest and PNS

• Specific marker for neuroectodermal neoplasms

• Consistently expressed in benign nerve sheath tumors, clear cell sarcoma, and melanoma

• SOX10 shows lower sensitivity for MPNST(30–50%)

SATB2 expression

spindled-to-epithelioid cells with scattered osteoclast- like

giant cells and scant osteoid deposition.

• SATB2(special AT-rich sequence-binding protein 2) is a nuclear matrix protein

• Plays a critical role in osteoblast lineage commitment

• SATB2 is a sensitive & specific immunohistochemicalmarker of osteoblastic differentiation in bone and soft tissue tumors

• SATB2 expression is also a feature of benign osteoblastic neoplasms, other sarcoma types with osteosarcomatous differentiation like dedifferentiated chondrosarcoma dedifferentiated liposarcoma

β-Catenin staining in desmoidfibromatosis

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

• It is consistently negative in other intra-abdominal mesenchymal neoplasms (including GISTs and smooth muscle tumors)

• it is not entirely specific

• A subset of solitary fibrous tumors (20– 40%) and low-grade myofibroblastic sarcomas (30%) also show nuclear staining

• Atypical lipomatous tumor and dedifferentiated liposarcoma are characterized by supernumerary ring and giant marker chromosomes, composed of amplified material from the long arm of chromosome 12 (q13~15)

• Within which several oncogenes are located, leading to overexpression of MDM2 and CDK4.

• Nuclear reactivity for MDM2 and CDK4 is highly Sensitive, but is not entirely specific

• Some spindle cell and pleomorphic sarcomas (such as MPNST, myxofibrosarcoma, and rhabdomyosarcoma) show nuclear staining in a subset of cases

• Combined positive staining for both MDM2 and CDK4 is much more specific.

MDM2 and CDK4 expression

MDM2 and CDK4 expression in liposarcomas

Well-differentiated liposarcoma (MDM2) Dedifferentiated liposarcoma(CDK4) Dedifferentiated liposarcoma (MDM2)so-called ‘inflammatory MFH

• SMARCB1 is a member of the SWI/SNF multisubunit chromatin remodeling complex

• It plays a fundamental role in regulating transcription.

• SMARCB1 is ubiquitously expressed in normal cells.

• Biallelic inactivation of SMARCB1 is a defining feature of malignant rhabdoid tumors

• Homozygous deletion of the SMARCB1 locus is common in epithelioid sarcoma(95%)

• Loss of SMARCB1 expression is seen in 50% of epithelioid MPNST and a subset of myoepithelial carcinomas, myxoid chondrosarcomas and poorly differentiated chordomas

SMARCB1 (INI1)-deficient tumors.

SMARCB1 (INI1)-deficient tumors.

Malignant rhabdoid tumor Conventional epithelioid sarcoma Proximal-type epithelioid sarcoma

(a) SDH-deficient GISTs arise in the stomach and show a multinodular growth pattern. (b) Similar to conventional GISTs, KIT is strongly positive. (c) Most SDH-deficient GISTs are dominated by epithelioid cytomorphology. (d) Loss of SDHB protein expression confirms the diagnosis. Note the granular cytoplasmic staining in endothelial cells, which serve as an internal control.

Succinate dehydrogenase (SDH)-deficient GIST

• The SDH complex participates in both the citric acid cycle (oxidation of succinate to fumarate) and the electron transport chain(complex II).

• Mutations in SDH subunit genes lead to loss of protein expression and enzyme function

TFE3 expression

(a) Alveolar soft part sarcoma composed of epithelioid cells with abundant eosinophilic cytoplasm and a nested architecture. (b) Strong nuclear staining for TFE3 is a characteristic finding.

• Alveolar soft part sarcoma harbors the translocation t(X;17), which leads to the ASPSCR1-TFE3 fusion and overexpression of the TFE3 protein

• TFE3 rearrangements have recently been identified in a small subset of PEComas and a distinctive subset of epithelioid hemangioendotheliomas

ALK expression in inflammatory myofibroblastic tumor.

IMTs composed of plump spindle cells arranged in loose fascicles with prominent stromal

lymphocytes. B) Cytoplasmic staining for ALK is observed in 50% of cases. (c) Epithelioid

inflammatory myofibroblastic sarcoma with amphophilic cytoplasm, prominent nucleoli, myxoidstroma,stromal neutrophils. (d) There is a characteristic nuclear membrane pattern of ALK staining

• ~50% of inflammatory myofibroblastictumors (IMTs) harbour rearrangements of the ALK locus

• Pattern of ALK staining appears to correlate with the fusion partner

• Most translocations (involving the fusion partners TPM3, TPM4, CARS, ATIC, SEC31A, and CLTC) result in cytoplasmic staining

• Nuclear membrane pattern of staining is seen with the RANBP2 fusion partner

• It is also positive in some RMS & MPNST

• Recently, a NAB2-STAT6 fusion has been identified by several independent groups as a consistent feature of solitary fibrous tumors

• So-called ‘meningeal hemangiopericytoma’ also harbors this fusion gene, supporting the classification of this tumor type with SFT

• NAB2-STAT6 fusion leads to high-level nuclear expression of the STAT6 protein

• By immunohistochemistry, nearly all cases of solitary fibrous tumor show strong nuclear staining for STAT6

DOG1 (discovered on GIST1) expression

a) Epithelioid GIST of the stomach with a PDGFRA mutation. (b) KIT is negative in tumor cells. Note the strong

membranous staining in occasional mast cells, which serve as an internal control.c) DOG1 is positive membranous

• Also known as ANO1 (anoctamin 1) and TMEM16A, this protein is a calcium-activated chloride channel expressed in normal interstitial cells of Cajal

• DOG1 was shown to be highly expressed in GIST by gene expression profiling

• DOG1 is a highly sensitive and specific marker for GIST

Monophasic synovial sarcoma composed of fascicles of

uniform spindle cells, Strong nuclear staining for TLE1 is

TLE1(transducin-like enhancer of split 1) expression

• TLE1 is a transcriptional corepressor that inhibits Wntsignaling

• Using gene expression profiling, TLE1 was found to be an excellent discriminator of synovial sarcoma from other sarcoma types

• TLE1 shows moderate-strong, diffuse nuclear staining in the majority of synovial sarcomas(80–90%)

• It is only positive in a small subset of MPNST and solitary fibrous tumors (usually with only weak staining)

• MUC4 is a high-MW transmembrane glycoprotein expressed on the surface of some glandular epithelial cell types.

• This epithelial mucin is highly expressed by low-grade fibromyxoid sarcoma (LGFMS)

• Characterized by the t(7;16) translocation, resulting in FUS-CREB3L2 rearrangement, or rarely t(11;16), resulting in FUS-CREB3L1 fusion

• Hybrid tumors with both LGFMS and SEF components, as well as ~70% of ‘pure’ SEF cases, are strongly positive for MUC4

MUC4 expression in fibroblastic sarcomas

MUC4 expression in fibroblastic sarcomas

(a) Low-grade fibromyxoid sarcoma showing a storiform-to-whorled growth pattern and bland spindle cell morphology. (b) Strong cytoplasmic staining for MUC4 is

highly specific for this tumor type among spindle cell neoplasms(c) Sclerosing epithelioid fibrosarcoma composed of cords of epithelioid cells embedded in a densely hyalinized stroma. (d) MUC4 is positive in most cases.

Novel immunohistochemical markers in soft tissue tumors

Approach to the diagnosis of soft tissue tumors

Sarcomas may be divided into groups based on their primary histologic growth pattern:

• Round Cell Soft Tissue Sarcomas

• Epithelioid Soft Tissue Sarcomas

• Fascicular Spindle Cell Sarcomas

• Pleomorphic Sarcomas

• Myxoid Soft Tissue Sarcomas

Round Cell Soft Tissue Sarcomas

-Keratins, EMA, Vimentin, Desmin, NSE, WT1

, SATB2+

Solitary fibrous tumor

Epitheloid Soft Tissue Sarcomas

,TFE3

, INI1 -

, ERG+

, ERG+

, DOG1+, SDHB -

, CK+, EMA+, Vimentin, CD99, Synp

, TLE1+

, EMA+/-, S100+/-, MUC4+

, S100+

Fascicular Spindle Cell Sarcomas

, TLE1+

, STAT6+

Actin+

, SOX10+, INI-/+,

Myxoid Soft Tissue Sarcomas

Actin+

Desmin+/-, calponin+/-

h-Caldesmon +

Pleomorphic Sarcomas

Role of genetic testing in soft tissue sarcoma

• Molecular genetics of STS has developed at a rapid pace in recent years.

• The more current textbooks including the WHO edition reserve specific sections to include recent cytogenetic and molecular data

• Diagnostic approaches were supplemented with reliable molecular diagnostic tools, detecting tumour type-specific genetic alterations

• Successful application of techniques to formalin-fixed paraffin- embedded tissue made it possible to subject a broader range of clinical material to molecular analysis

Sarcomas can be divided into two major genetic groups

• Soft tissue sarcomas with specific genetic alterations & relatively simple karyotypes:

• 15–20% bear specific reciprocal translocations (used as diagnostic markers)

• Specific somatic mutations (e.g., cKIT & PDGFR in GIST)

• Specific amplifications (e.g., MDM2 & CDK4 amplification in the liposarcoma)

• Soft tissue sarcomas with non-specific genetic alterations & complex karyotypes

• Genetic abnormalities like chromosomal numerical changes, translocations, gene amplifications or large deletions can be apparent at the cytogenetic level (karyotyping,FISH)

• Small deletions, insertions or point mutations, require molecular genetic techniques (PCR and sequence analysis)

Molecular genetic techniques

• The most common techniques currently used in molecular diagnostics include:

• Direct metaphase cytogenetics or karyotyping

• Fluorescence in-situ hybridization(FISH)

• Reverse transcriptase-polymerase chain reaction (RT PCR)

Comparison of the cytogenetic and molecular methods

• Comparative genomic hybridization, DNA chip microarray analysis, direct genome sequencing are currently remain in the realm of research tools.

• Next-generation sequencing (NGS) technologies also known as second-generation sequencing, deep sequencing, massively parallel sequencing

• It obtain simultaneously both width (i.e multiple nucleotide sequences are analysed at the same time) & depth (i.e each target nucleotide sequence is analysed several times)

• Allow detection of rare, mosaic variants in the analysis of genetic material.

New approach to identify gene fusions

Gene fusions in soft tissue tumours

• One-third of all sarcomas are characterized by specific recurrent chromosomal translocations

• In 1992 the first sarcoma-associated gene fusion the EWSR1–FLI1 chimera resulting from t(11;22)(q24;q12) in Ewing sarcoma was discovered

• New gene fusions were added at a fairly constant rate, and now amount to 94 fusions in more than 30 distinct entities

• Approximately 85-90% of EWS/PNET harbour t(11;22)

• This translocation juxtaposes the EWS gene from chromosome 22 and the FLI1 gene from chromosome 11,

• There is generation of a chimeric gene encoding a functional fusion protein composed of the transcriptional activating domain of EWS and the DNA binding domain of FLI1.

• The resultant fusion gene is oncogenic and includes the N-terminal transactivation domain of EWS and the C-terminal DNA binding domain of the FLI-1 gene.

FISH using the EWSR1 (22q12) dual colour, break-apart rearrangement probe

• The probe consists of a mixture of two FISH DNA probes

• The first is a 500-kb probe labelled in spectrum orange and flanks the 5’ side of the EWSR1 gene extending inward to intron 4

• The second probe is a 1100-kb labelled in spectrum green and flanks the 3’ side of the EWSR1 gene.

• The known breakpoints within the EWSR1 gene are restricted to introns 7’ to 10’

In normal cells , a two-signal pattern is expected to reflecttwo intact copies of EWSR1.In abnormal cells, a fusion signal, one green and one orange signal pattern will be expected.

• The Ewing sarcoma breakpoint region 1 (EWSR1; also known as EWS) represents one of the most commonly involved genes in sarcoma translocations

• It is involved in a broad variety of mesenchymal lesions which includes:• Ewing’s sarcoma,

• Desmoplastic SRCT,

• Clear cell sarcoma

• Angiomatoid fibrous histiocytoma

• Myxoid chondrosarcoma

• Subset of myxoid liposarcoma

• Myoepithelial tumours

• Low-grade fibromyxoid sarcoma,

• Sclerosing epithelioid fibrosarcom

• EWSR1 is a promiscuous gene that can fuse as 5′ partner with many different genes.

Common recurrent translocations in soft tissue tumours

Common recurrent translocations in soft tissue tumours

• Molecular results should be used as validation of the morphological differential diagnosis, corroborated with immunohistochemical findings and clinical information

• In spite of overwhelming cytogenetic and molecular data that gene fusions are highly specific markers, questioned have been raised about their specificity

• The molecular heterogeneity of fusion transcripts has been suggested to have a prognostic role in certain sarcoma types.

• In Ewing’s sarcoma, the presence of type 1 EWS-FLI1 fusion was shown to have a better survival benefit compared with other fusion transcript types

• Similarly, the presence of PAX7- FOXO1A was associated with a favourable prognosis in alveolar rhabdomyosarcoma, compared with the more common PAX3-FOXO1A variant

Sarcomas with oncogenic mutations

• Constitutive activation of either KIT or PDGFRA receptor tyrosine kinase by oncogenic mutations is a central pathogenic event in GISTs

• Malignant rhabdoid tumours show inactivating mutations of hSN5 ⁄ INI1 tumour suppressor gene on chromosome 22q11.

Sarcomas with complex karyotypes

• Two-thirds of soft tissue sarcomas lack a recurrent genetic signature and are characterized by numerous aberrations, including chromosomal losses and gains.

• Most of the adult spidle cell and pleomorphic sarcomas belong to this group

• There is high prevalence of p53 checkpoint alterations, including p53 inactivating mutations, homozygous deletion of CDKN2A, MDM2 amplifications

• There is markedly elongated and heterogeneous telomeres, that maintain telomeres in a telomerase-independent manner

• This mechanism of telomere dysfunction might contribute to the chromosomal aberrations found in complex sarcomas

Recently identified cytogenetic and molecular genetic aberrations

Recently identified cytogenetic and molecular genetic aberrations

Targeted therapies for sarcomas

• The modalities of treatment include surgery and radiotherapy for local control and chemotherapy for distant metastasis

• Recognition of different pathogenetic mechanisms, numerous targeted treatments are currently being investigated.

• Chemotherapeutic agents are designed to modulate, inhibit, or interfere with the function of specific molecular targets that are crucial to the malignancy of tumors

• In general, standard chemotherapy options are still quite limited for sarcoma

• The role of adjuvant chemotherapy in soft tissue sarcoma is still a matter of debate due to the inconsistent benefit noted in randomized prospective clinical trials

• The best and most well established example in sarcoma is the use of tyrosine kinase inhibitor as a targeted therapy for GIST