Pre-Operative Evaluation of Soft Tissue Sarcoma

Abstract

Soft Tissue Sarcoma (STS) is a group of heterogenous mesenchymal malignant neoplasms with variable clinical and biological behavior. Although most of the soft tissue tumors are benign in nature, a high degree of suspicion, based on clinical, radiological, cyto-histological and molecular studies, is required to diagnose STS early in its course. There are more than a hundred subtypes of STS reported in the literature. They have different prognostic implications, and often treated differently. In the last decade, owing to betterment of radiological and pathological reporting system, there has been a dramatic improvement in diagnosis and treatment of these tumors. This also led to overall improvement in awareness, and reduction in improper surgical treatment and delayed surgical referrals. However, a centralization of care is of pivotal importance for better management since STS is rare in general. The importance of multidisciplinary approach to the management of STS cannot be over emphasized. This should include a dedicated surgical team, in conjunction with radiology, pathology, radiation oncology, medical oncology, anesthesiology, physiotherapy, and nursing team. In the subsequent section we briefly discuss on the pre operative management of STS, focusing mostly on radiological and pathological evaluation.

1. Introduction

Soft Tissue Sarcomas (STS) represent a cohort of heterogenous tumors of mesenchymal cell origin (including fat, muscle, nerves, blood vessels, and other connective tissues) that account for 1% of all adult malignancies and hundreds of different histological and molecular subtypes. These different subtypes oftentimes behave differently and hence the evaluation and management of STS is diverse. And there comes the importance of Sarcoma Multidisciplinary Team (MDT) consisting of Surgical Oncologist, Orthopedician, Radiation Oncologist, Medical Oncologist, Onco-pathologist, Radiologist. The NICE guideline suggests referral to a specialist centre for any patient with a lump >5 cm, deep to fascia, fixed, immobile, painful, and increasing in size [1]. As a general rule, any indeterminate soft tissue mass is considered as STS, unless proven otherwise, and should be evaluated by Sarcoma MDT to determine the appropriate line of treatment. Owing to its rarity, evidence based management holds promising role in improving outcomes in STS. An analysis of data from 15,957 patients with STS in the National Cancer Database showed that NCCN guidelines based treatment, which largely relies on multidisciplinary approach to STS, improves survival outcomes [2]. This chapter encompasses the nuances of pre operative evaluation of STS in general.

2. Overview

Sarcomas can be broadly divided into soft tissue sarcoma and bone sarcoma. The true incidence of STS is underestimated, largely because of non inclusion of gastrointestinal stromal tumors (GIST) to the tumor registry before 2001. The anatomic site of origin has significant implications in management and prognosis of STS. The common site of origin includes extremities (43%), the trunk (10%), viscera (19%), retroperitoneum (15%), and head and neck (9%) [3]. Desmoid tumor or aggressive fibromatosis is a unique histological type associated with local invasion rather than distant metastasis. Rhabdomyosarcoma is the most common histological subtype among children and adolescents.

3. Risk factors

The evaluation of STS begins with the assessment of presence or absence of different risk factors associated with causation of STS. The risk factors are divided into modifiable and non-modifiable [4, 5].

The modifiable risk factors include

1. Prior exposure to radiation therapy

2. Chemical exposure (herbicides, such as agent orange)

The non modifiable risk factors include

Genetic syndromes as follows

Li- Fraumeni syndrome results from germline mutation of TP53 tumor suppressor gene. The syndrome results in multiple malignancies, namely STS, osteosarcoma, breast cancer, leukemia, brain tumors, adrenocortical carcinoma. The incidence of STS in this mutation ranges from 12–21% and diagnosed in early life as compared to sporadic STS [6]. Patients suspected to be suffering from this syndrome or with a known family history of this syndrome require genetic counseling prior to initiation of therapy for STS.

Familial Adenomatous Polyposis (FAP) results from germline mutation of adenomatous polyposis coli (APC) gene on chromosome 5q21. This autosomal dominant colorectal cancer syndrome is also associated with desmoid tumor (aggressive fibromatosis). The prevalence of desmoid tumor in this syndrome is much higher than that of general population [7]. The most common location of desmoid in FAP is intra-abdominal and abdominal wall (53% and 24%, respectively) which often makes surgical resection challenging. Evaluation for FAP or Gardner’s syndrome is recommended for patients with desmoid tumor.

Carney- Stratakis syndrome is another autosomal dominant condition characterized by GISTs and paragangliomas. Germline loss-of-function mutations of succinate dehydrogenase (SDH) gene subunits (SDHB, SDHC, and SDHD) has been identified to be causative of this syndrome. GISTs associated with this syndrome are negative for SDHB, in contrast to GIST with KIT or PDGFRA mutations or sporadic GIST [8].

Hereditary Retinoblastoma, caused by germline mutation of RB1 tumor suppressor gene, results in higher risk of STS. Leiomyosarcoma (LMS) is reportedly the most common association, with 78% of LMS diagnosed 30 or more years after diagnosis of retinoblastoma [9].

Neurofibromatoses result from mutations in neurofibromin 1 (NF1) or neurofibromin 2 (NF2). Approximately 5% of NF patients develop STS, most commonly malignant peripheral nerve sheath tumors (MPNSTs) [10].

4. History and physical examination

Some of the STS are more common in certain age group than other. Gastrointestinal Stromal Tumor (GIST) is considered to be the most common STS in adults. Other common histological types include undifferentiated pleomorphic sarcoma (UPS), liposarcoma (LS), leiomyosarcoma (LMS), and myxofibrosarcoma (MFS). The commonest histology in children is rhabdomyosarcoma (RMS). Some of the common sarcomas of early adulthood are synovial sarcoma, alveolar soft part sarcoma, and Ewing sarcoma.

The classical history of a soft tissue sarcoma patient is a slow growing lump, increasing in size, over a period of time. Often these lumps are associated with pain. The detailed history of pain, such as rest pain, pain on activity, radiation of pain, are significant. Some tumors may show features of rapid growth which usually indicate malignant transformation or intra tumoral hemorrhage. The history of trauma, which mostly is circumstantial, is relevant as this often serves as the first point when the patient comes to know about the tumor. Also, trauma helps exclude non-malignant differentials of a lump. Change in size of the lump often indicates inflammatory masses and lymph nodes and helps excluding STS.

Physical examination should focus on estimation of the size of the mass, its location with respect to the deep fascia, its mobility and consistency. The mass should be palpated all around to determine the anatomical boundaries with respect to the compartments of the limb. Tenderness over the mass usually points towards inflammatory process. The auscultatory findings of pulsatile flow should suggest possibilities of pseudoaneurysm or vascular malformation/tumors. Sensory/motor dysfunction along the course or distal to the tumor usually indicates involvement or compression of a nerve by the tumor. A positive Tinel’s sign indicates towards a nerve sheath tumor or nerve compression. A distal limb swelling may indicate venous stagnation or lymphatic obstruction. Proximal lymph nodal basins should be carefully examined to look for lymphadenopathy.

5. Imaging

Following a detailed a history to exclude presence of different risk factors and clinical examination focused on the local examination of the tumor, the next investigation to stage the disease is the imaging. Imaging plays an important role in diagnosis, guiding biopsy, pre treatment staging, surgical planning, and follow up. Although most of the STS have non specific imaging characteristics, a few histological subtypes can be diagnosed with specific imaging features of the primary and metastases.

5.1 Adipocytic tumors

1. Well Differentiated Liposarcoma (LPS) and Atypical Lipomatous Tumors (ALT)- these tumors have predilection for extremities, retroperitoneum, paratesticular and inguinal regions [11]. These tumors have predominantly fat components in imaging. Features that favor liposarcoma over lipoma include age greater than 60 years, lesion size more than 10 cm, lower extremity location, presence of thickened septations (>2 mm), nodular enhancing foci, and solid components. The sclerosing variant of well differentiated LPS are mostly seen in retroperitoneum and have predominantly non fatty components.

2. Dedifferentiated Liposarcoma- these are mostly located in retroperitoneum, and rarely in extremities and mediastinum. It can be found in the primary well differentiated LPS or its recurrence or metastasis. They resemble undifferentiated high grade pleomorphic sarcoma and may exhibit heterogenous differentiation, such as, myogenic or osteo/chondromatous elements. On imaging, they have non fatty components, often greater than 1 cm, often showing enhancement. With the higher degree of dedifferentiation, the proportion of lipomatous component comes down progressively. Distant metastases are more common than well differentiated LPS, and mostly occur in liver and lungs.

3. Myxoid Liposarcoma- the most common location is at the deep soft tissue of thigh. They tend to occur in young to middle aged adults. On imaging, they have a well circumscribed, multilobulated, septated appearance. The myxoid component takes very high signal intensity in T2 weighted MRI, with heterogenous enhancement pattern. The high grade tumors usually show more than 10 cm size, deep location, lack of lobulations, and more than 5% fatty component [12, 13]. Myxoid LPS has a tendency to metastasize to extrapulmonary sites, especially to paraspinal region, intramuscular fat pad, bone, retroperitoneum, and the opposite extremity. Whole body MRI is an useful tool for screening of bony and soft tissue metastasis in myxoid LPS.

4. Pleomorphic Liposarcoma- these are the least common subtype of LPS and tend to occur in elderly patients, specially in deep soft tissue of the extremities. They have a high propensity for early metastasis and have a poor prognosis. The imaging usually shows features of aggressive sarcoma with evidence of local invasion having little fat component.

5.2 Fibroblastic/myofibroblastic tumors

1. Dermatofibrosarcoma Protuberans- this rare form comprises of 6% of all STS. They are more common in men and in fourth and fifth decade. They have t(17;22) translocation, resulting in platelet derived growth factor receptor activation. The most common site of occurrence is the trunk. In 20% cases there is fibrosarcomatous transformation [14]. The typical MRI findings include a lobular or nodular enhancing intermediate signal intensity lesion with focal protuberance. T2 hyperintensity is noted in myxoid lesions. Hemorrhage and necrosis indicates fibrosarcomatous transformation.

2. Myxofibrosarcoma- it is more common after sixth decade and extremity is the most common location (75%). Most are subcutaneous tumors. Because of myxoid components, they are typically hyper enhancing in T2 weighted MRI. Often there are septations, necrosis, and hemorrhage. T2 hypointense pseudocapsules may be present. A characteristic feature is unencapsulated margin and infiltrative growth pattern along the fascial planes, and this explains the high risk of local recurrence post resection. This infiltrative nature is visible on MRI as a high signal ‘tail sign’ that discriminates this tumor from other myxoid neoplasms.

5.3 Smooth muscle tumors

Leiomyosarcoma (LMS): they account for about 9% of STS. The commonest sites of involvement are uterus, retroperitoneum. They are the most common sarcoma of large blood vessels. On MRI, they show non specific features, such as T1 iso-intensity with moderate hyper intensity in T2. Hemorrhage, necrosis, cystic changes are common for larger tumors [15]. They often show features of calcification and ossification.

5.4 Skeletal muscle tumors

Rhabdomyosarcoma (RMS): it is the most common STS of childhood. In children, the most common site of affection is head and neck parameningeal region, while in adults the commonest site of involvement is extremities followed by genitourinary system. There are three histological subtypes. The commonest one is embryonal type (50%) occurring in the first decade of life, and affects head and neck and genitourinary system. The alveolar type (30%) has more preponderance to affect the trunk and extremities of adolescents. They also tend to affect the lymph nodes. The pleomorphic subtype is common in adults more than 45 years and commonly affect lower extremities. Embryonal RMS usually presents with poorly circumscribed heterogenous mass with moderately high signal intensity in T2 weighted images [16]. The botryoid type is characterized by multiple ring enhancing regions inside the mass. There may be features of infiltration to the surrounding bones. Alveolar RMS present as infiltrative heterogenous mass with area of necrosis. They show moderately high signal intensity in T2 images. The pleomorphic type shows marked high signal intensity in T2 images with features of infiltration.

5.5 Vascular tumors

Angiosarcoma: the majority of angiosarcoma are subcutaneous in origin, with less than 25% arising from deep soft tissue. Factors increasing the risk of angiosarcoma include chronic lymphedema, radiation exposure, familial syndromes (e.g., neurofibromatosis type 1, Klippel-Trenaunay-Weber syndrome), and implants. These are tumors with very aggressive biology with high potential for locoregional and distant metastases. MR signal characteristics include intermediate on T1 and heterogeneously high on T2 images. Areas of high signal on T1 usually suggests intra tumoral hemorrhage. Deeper tumors may show flow void, but this is typically absent in subcutaneous tumors.

5.6 Nerve sheath tumors

These include benign tumors, such as schwannoma and neurofibroma, and malignant tumors, such as Malignant Peripheral Nerve Sheath Tumors (MPNST). MPNSTs may arise de novo, or in the background of benign neurofibromas in the setting on NF1. MPNSTs account for about 5–10% of all STS and occur in fourth to sixth decade of life with equal sex predilection, except for those arising in the background of NF1 where it appears early in life and more common in male (about 80%) [17]. Some MPNSTs have rhabdomyoblastic components inside the tumor and are classified as malignant triton tumor, which manifest an aggressive course and poorer outcome. The most common nerves involved are sciatic nerve, brachial plexus, and sacral plexus. These tumors show non specific imaging features like intermediate signal intensity on T1 and iso to high signal on T2 weighted images. They often share imaging characteristics of benign neurogenic tumors such as fusiform appearance around an involved nerve, split fat sign, bright rim sign, fascicular sign, and atrophy of the supplying muscle owing to denervation. Clinical pictures such as high growth rate, size more than 5 cm, infiltrative margin favor the diagnosis of malignant tumor more than benign. Imaging features indicative of malignancy are heterogeneous high signal on T1, irregular peripheral enhancement pattern, and peritumoral edema [18].

5.7 Tumors of uncertain differentiation

1. Synovial Sarcoma (SS): these account for 5–10% of STS and usually manifest in young adults. They are pathologically classified as monophasic (spindle cell component), biphasic (spindle cell and epithelial components), and poorly differentiated subtypes. The t(X;18) translocation is characteristic and seen in 95% of the tumors. The most common site of origin is extremity, especially around the knee and adjoining tendon sheath. On imaging, SS are septated multilobulated mass with heterogenous signal intensity on T1 and T2 images, due to cystic changes, necrosis, hemorrhage, calcification. They may demonstrate ‘fluid- fluid levels’ due to layering hemorrhage, and ‘bowl of grapes’ due to T2 hyperintense lobulations on the background of hypointense septa [19]. Aggressive tumors show signs of invasion to bone and infiltration of adjacent organs. They have a very rate of lung metastasis as well as lymph nodal metastasis.

2. Alveolar Soft Part Sarcoma (APSS): these rare tumors are usually seen in children and young adults, and tend to occur more in lower extremities. Owing to highly vascular nature, they often present as pulsatile mass with audible bruits. On imaging, they appear as well circumscribed lobulated masses with moderately high signal intensity on T1 and T2 images and marked contrast enhancement. They often have internal signal voids due to intra tumoral vessels [20]. Most present with lung metastasis at diagnosis. Other sites of metastasis include lymph nodes, bones, and brain. Despite having an aggressive biology, they susually have a good survival.

3. Extraskeletal Ewing Sarcoma (EES): they belong to the Ewing Sarcoma (ES) family of tumors, that include ES, EES, Primitive Neuroectodermal Tumors (PNET), and Askin tumor. ES belongs to small round blue cell tumor family, arising from neuroectodermal cells, with classical t(11;22) translocation. They arise mostly from deep soft tissue of extremities, retroperitoneum, chest wall, and paravertebral regions (most commonly in cervical and sacral spinal level). On imaging, they have a bulky heterogenous appearance with adjacent organ invasion. They are hypo or iso intense to the skeletal muscle on T1 and heterogeneously hyperintense on T2 images, with frequent occurrence of central necrosis [21]. The most common sites of metastasis include lungs, lymph nodes, and bones.

4. Extraskeletal Osteosarcoma (EO): they are very rare and very aggressive. They tend to occur in post radiation setting, in fifth decade and later. The commonest site of involvement is thigh, followed by upper extremity, retroperitoneum and trunk. The MRI findings include well circumscribed, inhomogeneous mass on T1 and T2, with or without heterogeneous contrast enhancement and often with pseudocapsule formation. Mineralization is seen n 50–70% cases, and may cause signal void [22]. Aggressive tumors may have intra tumoral hemorrhage, necrosis. They have a high propensity for metastasis and poor overall survival.

5. Aggressive Angiomyxoma: they are rare locally aggressive tumors most commonly arising from perineum and lower pelvis. They often present late due to displacement of adjacent organs without symptoms. Owing to myxoid matrix, they are T2 hyper intense. The presence of fibrovascular stroma leads to swirling or laminated appearance [23].

6. Desmoplastic Small Round Cell Tumor: these rare tumors arise from peritoneal layers of younger adults, more commonly in male. They belong to the family of small round blue cell tumors. The common imaging appearance include bulky, heterogenous peritoneum based masses, without distinct site of origin. The pelvis and paravesical regions are frequent sites of affection. Ascites is common.

7. Solitary Fibrous Tumor (SFT): these rare tumors appear in middle aged individuals without sex predilection. Histological hallmark of these tumors are CD34 positivity (seen in 80–100% cases) and over expression of STAT6 protein. The commonest site of origin is the pleura and about 20% cases are malignant. The extra-pleural tumors usually originate from retroperitoneum, pelvis, proximal extremity, and abdominal wall. On MRI, these are well circumscribed, lobular masses and having inhomogeneous signal intensity on T2 images. The fibrous and hemorrhagic component gives a T2 hypo intensity while the myxoid and cystic component gives T2 hyper intensity images.

8. Gastrointestinal Stromal Tumor (GIST): GISTs are the most common mesenchymal tumors originating from GI tract. They are believed to grow from the intestinal cell of Kajal. Pathologically they are characterized by activating mutation of tyrosine kinase receptors, namely c-kit (CD117)or platelet derived growth factor alpha. On imaging, GISTs present as predominantly exophytic soft tissue masses arising from the bowel wall with variable areas of hemorrhage and necrosis [24]. The most common site of origin is stomach. Metastasis is mostly limited to liver and peritoneum, however lymph nodal metastasis is noted in succinate dehydrogenase deficient GISTs.

6. Biopsy

The treatment of soft tissue sarcoma is dependent on the histological type and hence the importance of a correct biopsy cannot be over emphasized. The goal of biopsy is to provide adequate tissue for histology and immunohistochemistry. Furthermore, the biopsy tract is often the place for seedling of cancer cells, so the biopsy should always be planned in a way so that the biopsy site and the biopsy tract can be taken out with the tumor during definitive resection.

Soft tissue sarcomas (STS) comprise of neoplasia arising from soft tissues which are mostly uncommon tumors of diverse histology, different biology and varied outcomes. Recent advancements in the field of pathology with the advent of immunohistochemistry (IHC), cytogenetics and molecular genetics have caused change in the classification and diagnosis of STS. It has also changed the clinical management and prognosis of these tumors.

The WHO classification of STS considers the clinical, histological and genetic factors and it divides STS into four categories viz. benign, intermediate (locally aggressive), intermediate (metastasizing) and malignant [25, 26].

The benign tumors usually do not recur while the intermediate (locally aggressive) tumors tend to recur locally and follow an infiltrative destructive growth pattern. However, they usually lack the potential to metastasize. On the other hand, the intermediate (metastasizing) tumors in addition to being locally aggressive, have the ability to metastasize in few cases, the risk of it being <2% and is cannot be predicted by its histomorphology. Malignant soft tissue tumors show a significant ability of distant metastasis, which ranges from 20% to almost 100% depending on the histological type and grade [26, 27].

Biopsy of STS is done by either of open or closed approach. While an open biopsy usually requires an operating room for obtaining tissue, a closed biopsy is usually an out patient procedure that relies on taking tissue using core biopsy needle with or without image guidance.

A blind biopsy without image guidance is usually the choice for superficial mass which are easily palpable and the most representative area (solid part of a heterogenous mass) is easily accessible to the clinician obtaining biopsy. The mass must always be away from any critical underlying structure to prevent inadvertent injury. In all other cases an image guided biopsy would be justified over a blind technique.

Close biopsies are associated with less morbidity, but the yield of tissue is less. It can be in the form of fine needle aspiration cytology (FNAC) or core needle biopsy (CNB). FNAC has limited use in STS due to the fact that it gives only small sample of cells from the tumor and often it is not possible to run extended batteries of stains and cytogenetics to determine the accurate subtype.

Core needle biopsy (CNB), on the other hand, provides pathologist enough tissue sample to determine the exact histopathological subtype. Also it provides adequate material for immunohistochemistry and cytogenetics.

Irrespective of the biopsy technique employed, the biopsy track must always be planned in a way to incorporate during the surgical resection of the mass. Also, the biopsy track must not contaminate multiple compartments, joint spaces, and neurovascular structures.

Open biopsies are divided into incisional and excisional biopsy. Although excisional biopsy is generally not recommended for STS, incisional biopsy provides sufficient tissue for subtyping STS and has the advantage of immediate frozen section analysis to confirm the presence of representative tissue. An open biopsy incision should be planned after consultation with the primary surgeon who subsequently operates on the patient. The wound must be closed after securing proper hemostasis to prevent formation of post operative hematoma which would otherwise contaminate the adjacent tissue planes unnecessarily.

6.1 Grading

The two predominant grading systems for STS are the Fédération Nationale des Centres de Lutte Contre le Cancer (FNCLCC) and the National Cancer Institute (NCI) systems [28, 29]. Each of these systems consists of three grades, which rely on factors such as mitotic activity, necrosis, and differentiation. The NCI system additionally takes into account cellularity and pleomorphism for specific subtypes of sarcoma. The grading system correlates to the prognosis of the disease. The TNM staging recommends the FNCLCC system for classification into ‘high grade’ and ‘low grade’ [30, 31]. The FNCLCC grading system is shown in Table 1.

Tumor differentiation
Score 1	Sarcomas closely resembling normal adult mesenchymal tissue (e.g. well differentiated liposarcoma and leiomyosarcoma)
Score 2	Sarcomas for which histological typing is certain (e.g. myxoid liposarcoma & conventional leiomyosarcoma)
Score 3	Embryonal and undifferential sarcomas, Pleomorphic sarcomas, synovial sarcomas, osteosarcomas, PNET)
Mitotic count
Score 1	0–9 mitoses per HPF
Score 2	10–19 mitoses per HPF
Score 3	> = 20 mitoses per HPF
Tumor necrosis
Score 0	No tumor necrosis
Score 1	Less than or equal to 50% tumor necrosis
Score 2	More than 50% tumor necrosis
Histological grade
Grade 1	Total score 2, 3
Grade 2	Total score 4, 5
Grade 3	Total score 6, 7, 8

Table 1.

Histological grading according to FNCLCC.

6.2 Morphological categories

Apart from grading, histopathological examination of STS also includes architectural pattern, the appearance of the cells and the stromal characteristics. This creates several different categories which are classified based on morphological features as well as immunohistochemical markers. The classification is as demonstrated in Table 2.

Morphological category	IHC parameters
Fascicular spindle cell sarcomas
Fibrosarcoma	Vimentin
Leiomyosarcoma	SMA, HHF 35, Calponin, Desmin ±
Spindle cell RMS	Desmin+, Myogenin+
Synovial sarcoma	S-100±, EMA+
MPNST	S-100+, EMA−
Solitary fibrous tumor	CD34+, CD99−, CD31−
Myxoid Soft Tissue Sarcomas
Myxoid liposarcoma	MDM2+,CD34±, novel IHC antibody to the TLS/EWS-CHOP chimeric oncoproteins
Myxoid chondrosarcoma	Vim+, Synaptophysin±, EMA±
Myxoid DFSP	CD34
Myxoid MFH (myxofibrosarcoma)	CD34+, HMGA1 and HMGA2
Botryoid Embryonal RMS	Desmin, Myogenin
Myxoid leiomyosarcoma	SMA, HHF 35, Desmin, Myogenin
Epitheloid Soft Tissue Sarcomas
Alveolar soft part sarcoma	Desmin, SMA
Epithelioid sarcoma	CK, EMA, Vimentin, CD34±
Epithelioid angiosarcoma	CD31, Factor VIII, CD34, FLI-1
Epithelioid haemangioendothelioma	CD31, Factor VIII, CD34, FLI-1
Extra gastrointestinal stromal tumor	CD117, CD34±
Malignant Rhabdoid tumor	Polyphenotypic, Loss of INI1 protein
Malignant mesothelioma	Calretinin, Thrombomodulin
Synovial sarcoma	EMA, Cytokeratin, S100±
Sclerosing epithelioid fibrosarcoma	Vimentin
Clear cell sarcoma	HMB45, Melan1 EWSR1-ATF fusion
Round Cell Soft Tissue Sarcomas
Alveolar RMS	Desmin, Myogenin
Desmoplastic small round cell tumor of childhood	Polyphenotypic
Embryonal RMS	Desmin, Myogenin
Extra skeletal ES/PNET	CD99, FLI-1
Round cell liposarcoma	S-100
Small cell osteosarcoma	Vimentin
Malignant hemangiopericytoma	CD34
Pleomorphic Sarcomas
Pleomorphic undifferentiated sarcoma	Vimentin
Malignant fibrous histiocytoma	Alpha 1 antitrypsin, alpha-1-antichymotrypsin
Pleomorphic liposarcoma	MDM2 and CDK4
Pleomorphic RMS	Desmin, Myogenin
Pleomorphic MPNST	S100
Pleomorphic leiomyosarcoma	SMA, SMA, Desmin
Pleomorphic angiosarcoma	CD31, Factor VIII, CD34, FLI-1
Chondro-Osseous STS
Mesenchymal Chondrosarcoma	S-100
Extra skeletal osteosarcoma	Vimentin
Clear Cell Lesions
Clear cell sarcoma of soft tissue	S-100, HMB45, NSE, CD57, EWSR1-ATF fusion gene
Clear cell myomelanocytic tumor	HMB45, MelanA±, SMA±

Table 2.

Morphological categories of STS.

Histological classification and diagnosis of STS is quite complex. It is sometimes difficult to precisely classify the tumor based on fine needle aspiration (FNA) and core biopsy specimens. The role of frozen section intraoperatively is also limited and only provides information about the margin status and that tumor tissue has been obtained.

In certain cases, a few reactive processes may mimic sarcomas. The distinction with reactive cells is made on the fact that the latter usually does not demonstrate any atypical mitosis or nuclear atypia which is characteristic of a neoplastic cell. The reactive cells have large vesicular nuclei, prominent nucleoli and basophilic cytoplasm.

In terms of grading, histopathological information obtained by small biopsies (FNA/core needle) can sometimes be inaccurate. This may cause a high-grade lesion being diagnosed as low grade because features like necrosis may be missed. Thus, proper classification is sometimes only possible on open excision biopsies or resected specimens. Grading of STS also becomes unreliable if chemotherapy or radiotherapy has been administered prior to biopsy.

6.3 Immunohistochemistry

Immunohistochemical staining has played a pivotal role in enhancing the precision of STS diagnosis, especially given that several histologic subtypes exhibit distinct chromosome translocations and gene rearrangements.

Some of them include Ewing’s sarcoma, t(11,22); synovial sarcoma, t(X,18); myxoid liposarcoma, t(12,16); and clear cell sarcoma, t(12,22) [32].

The primary approach in immunohistochemistry (IHC) involves two key steps: first, the exclusion of non-mesenchymal tumors, and second, the determination of the cell lineage of any identified mesenchymal tumors. This process necessitates the use of a panel of diverse immunostains rather than relying on a single marker to minimize the risk of misdiagnosis due to unusual antigen expression, such as cytokeratin in angiosarcoma [33]. Employing a predefined and thoughtfully selected small panel based on distinct patterns is recommended, as it offers a more efficient and cost-effective approach. The initial selection of IHC markers should consistently include a broad keratin (pancytokeratin), S100, and vimentin. A positive keratin result suggests a primary carcinoma, while a positive S100 stain should trigger the application of additional melanoma markers. Leukocyte common antigen (LCA) and CD30 are pivotal markers for distinguishing Hodgkin’s lymphomas, large cell lymphomas (including anaplastic large cell lymphoma), and follicular dendritic cell tumors [33].

A unique soft tissue sarcoma showing both epithelial and mesenchymal differentiation is synovial sarcoma. IHC is useful in the diagnosis and to distinguish the monophasic spindle cell from the other sarcomas. Cytokeratins and EMA are strongly positive in most cases and is usually co-expressed with vimentin. CD34 is positive in around 50% cases. A strong CD99 membrane positivity is usually seen in most Ewing’s sarcoma/Primitive Neuroectodermal Tumors, though it tends to be more sensitive than specific [34].

Though histopathology and immunohistochemistry can diagnose a majority of soft tissue sarcomas, it is to be noted that the results should be considered in the context of all available data since there is a tendency of aberrant antigen expression in soft-tissue tumors. There are a variety of pitfalls in the diagnosis of STS including technical factors and there is even an estimate that IHC adds confusion to the diagnostic process in 5–10% cases [35].

6.4 Detection of fusion genes

The detection of fusion genes in soft tissue sarcomas typically involves various laboratory techniques and tests (Table 3). Here are some common methods for detecting fusion genes:

1. Fluorescence In Situ Hybridization (FISH): FISH is a molecular cytogenetic technique that uses fluorescent probes to detect specific DNA sequences. It can identify chromosomal rearrangements that result in fusion genes. This method is commonly used in clinical diagnostics for detecting fusion genes in soft tissue sarcomas.

2. Reverse Transcription Polymerase Chain Reaction (RT-PCR): RT-PCR is a molecular biology technique that allows for the amplification and detection of RNA molecules. It is commonly used to detect fusion transcripts in sarcomas. Specific primers designed for the known fusion gene breakpoints are used to amplify and identify the fusion transcript.

3. Next-Generation Sequencing (NGS): NGS is a high-throughput sequencing technology that can identify fusion genes by sequencing the entire genome or transcriptome. This approach is particularly useful for discovering novel or rare fusion events and provides comprehensive genomic information.

4. Immunohistochemistry (IHC): In some cases, immunohistochemistry can indirectly suggest the presence of fusion genes. Specific antibodies can target fusion protein products or surrogate markers associated with fusion genes, aiding in diagnosis.

5. Cytogenetic Analysis: Traditional cytogenetic techniques, such as karyotyping and G-banding, can reveal chromosomal abnormalities that may indicate the presence of fusion genes. These methods are particularly valuable for detecting large chromosomal rearrangements.

6. RNA Sequencing: RNA sequencing can provide valuable information about the transcriptome, including the presence of fusion transcripts. It is especially useful for discovering new fusion events and understanding the functional consequences of fusion genes.

7. Array Comparative Genomic Hybridization (aCGH): aCGH can detect genomic imbalances, including chromosomal gains or losses, which may be indicative of fusion genes in some cases.

STS type	Fusion gene	Chromosomal location	Clinical significance
Ewing sarcoma	EWSR1-FLI1	22q12.2; 11q24.3	Most common fusion gene in Ewing sarcoma.
Alveolar rhabdomyosarcoma	PAX3-FOXO1 or PAX7-FOXO1	2q36.1; 1p36.13; 13q14.11	Found in most cases of alveolar rhabdomyosarcoma.
Synovial sarcoma	SS18-SSX1 or SS18-SSX2	18q11.2; X chr; X chr	Specific translocation seen in synovial sarcoma.
Myxoid liposarcoma	FUS-DDIT3	16p11.2; 12q13.12	Characteristic fusion gene in myxoid liposarcoma.
Dermatofibrosarcoma protuberans	COL1A1-PDGFB	17q21.33; 22q13.1	Common fusion gene in dermatofibrosarcoma protuberans.
Clear cell sarcoma	EWSR1-ATF1	22q12.2; 12q13.2	Associated with clear cell sarcoma of soft tissue.
Desmoplastic small round cell tumor	EWSR1-WT1	22q12.2; 11p13	Identifying fusion gene in desmoplastic small round cell tumor.
Infantile fibrosarcoma	ETV6-NTRK3	12p13.2; 15q25.3	Occurs in infantile fibrosarcoma cases.
Inflammatory myofibroblastic tumor	ALK	2p23	ALK gene rearrangements in this tumor type.

Table 3.

STS with fusion genes.

The choice of detection method often depends on the specific fusion gene of interest, the available resources, and the laboratory’s expertise. A combination of these techniques may be used to accurately identify fusion genes in soft tissue sarcomas, aiding in both diagnosis and potential targeted therapy decisions.

7. Predictive nomograms

Despite curative intent treatment of STS, approximately 25% of patients develop metastatic disease in long run [36]. The incidence reaches 50% for those with high risk tumors (size >5 cm, location deep to deep fascia, high grade histology) [37, 38]. The ability to predict recurrence and survival in long run help us make the treatment planning more rational. It also makes the patient more compliant with the treatment decision making. Therefore, prognostic nomograms incorporating clinical parameters such as tumor site, size, histological pattern, grade, patient age, performance status, are useful tool for treatment decision making, patient counseling, meeting patient’s expectations, post treatment follow up strategy making, and also for conducting clinical trials. The first nomogram introduced for STS was from the Memorial Sloan Kettering Cancer Center (MSKCC) group and is widely known as MSKCC Sarcoma Nomogram. It incorporated five covariates, including age at diagnosis, tumor size, histological subtype, histological grade, and anatomical site. It was aimed at determining 12-year sarcoma specific death probability for low and high grade tumors.

In 2003, the MSKCC group produced another nomogram to predict 5-year sarcoma specific death probability for locally recurrent disease based on the same covariates. Later it was understood that the anatomical site plays a major role in predicting prognosis of sarcoma, and hence several site specific nomograms were introduced to predict locoregional recurrence, disease free survival (DFS), and overall survival (OS). Anaya et al. described a nomogram which took histology, completeness of resection, age, multifocality, tumor size, and presentation as covariates [39]. In a nomogram described by Ardiono et al., histology, FNCLCC grade, size, surgical resection margin, and age were taken as covariates [40]. Tan et al. described another nomogram which included histology, extent of resection, number of organs resected, size, and radiation [41]. In 2013, Gronchi et al. described a nomogram studying more than 500 patients [42]. This nomogram was externally validated and endorsed by the American Joint Committee on Cancer (AJCC) staging system for retroperitoneal sarcoma. This nomogram included FNCLCC grade, tumor size, histology, age, multifocality, and extent of surgical resection into account. This predicts 7 year OS for different histological subtypes, including dedifferentiated liposarcoma, leiomyosarcoma, malignant peripheral nerve sheath tumor, solitary fibrous tumor, undifferentiated pleomorphic sarcoma, well differentiated liposarcoma etc.

One of the major limitations of using nomograms is that they predict the survival based on post operative findings, and hence the ability to determine the pre operative prediction of survival is limited.

8. Centralization of care

Soft tissue sarcoma has more than a hundred histological and molecular subtypes. They often behave differently from one another. And the heterogeneity is not just confined to diagnosis, but also in treatment decision making and prognosticating the disease. It is a proven fact that the outcome over short and long term is better for institutes dedicated to treatment of similar malignancies. The treatment decision is entirely based on multidisciplinary approach, which necessarily includes surgical oncologist, orthopedic oncologist, radiation oncologist, medical oncologist, dedicated radiologist and pathologist, physiotherapist, rehabilitation therapist, and dedicated nursing team. There are studies to support the better short term as well as long term outcomes when the patients of STS are treated in high volume centers having a dedicated sarcoma team. Keung et al. reported in their study of more than a thousand retroperitoneal sarcoma cases that patients treated at high-volume centers had lower 30-day readmission, lower 30-day and 90-day mortality, and longer median and 5-year overall survival [43]. These findings were similar to a French study of over thirty-five thousand patients showing that those treated at specialized sarcoma referral centers had a low risk of local relapse, progression, and death (hazard ratio [HR], 0.64, 0.83, and 0.68, respectively; all P < .001) [44, 45]. Also the centralisation of care would enable us to perform multi-institutional studies to answer the unmet needs in the management of STS which ultimately benefits the patients. We live in the era of personalized cancer care, and treatment of STS has undergone a paradigm shift in a decade time, fundamentally based on the same ideation.

9. Conclusion

STS accounts for 1% of all malignancies. Hence, having a robust data on management strategy is a difficult task. However, with the advancement of different treatment modalities, there has been a paradigm shift in the management of these tumors. The sarcoma specific centers having multidisciplinary approach to personalized cancer care for STS is definitely the way forward. Continued collaborative efforts from these centers will allow future studies sufficiently powered to generate further evidence and betterment of STS specific treatment.

Conflict of interest

The authors declare no conflict of interest.