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What are soft tissue tumors?

Soft tissue tumors are defined as the lesions of any non-epithelial tissue cells other than bone, cartilage, central nervous system (CNS), hematopoietic, and lymphoid tissues.

According to WHO the soft tissue is defined as all “non-epithelial extra-skeletal tissue cells present in the body except the reticuloendothelial system, the glia and the supporting tissues of specific organs & viscera”.

The soft tissue tumors are classified according to the tissue they recapitulate (summarize) to the tissue such as muscle, vessels, fat, fibrous tissue, & nerves in the body. Benign soft tissue tumors are in regards to 100 times more common than sarcomas. 

The sarcomas of soft tissue tumors rarely appear from malignant transformation of pre-existing benign tumors & sarcomas originate from the primitive mesenchymal cells and usually metastasize via hematogenous routes, making the lung, brain, liver, and skeleton common sites of dissemination.

Soft tissue tumors (sarcomas) generally are treated with surgical excision (frequently limb-sparing), with the help of irradiation and systemic therapy reserved for large high-grade tumors.  


General features of soft tissue tumors

  • Superficially located tumors tend to be benign tumors and deeply located lesions are generally malignant.
  • Large size tumors are normally malignant in nature than small ones.
  • Rapidly growing tumors frequently behave malignantly than those that slowly develop.
  • Frequently increased vascularity which is malignant while selective avascular is benign tumors.
  • Soft tissue tumors may arise everywhere in the body but in general, more common sites are lower extremity (about 40%), upper extremity (about 20%), trunk, and retroperitoneum (about 30%), and head and neck (about 10%).
  • Soft tissue tumor is more frequently affected in males than females.
  • Nearly 15% of tumors generally occur in children but certain sarcomas tend to appear in certain age groups for example rhabdomyosarcoma in childhood, Synovial sarcoma more commonly occurs in young adulthood, and liposarcoma and pleomorphic fibroblastic or undifferentiated sarcomas more commonly occur in later adult life.

What causes soft tissue tumors? (etiology and pathogenesis)

The etiology of soft tissue tumors remain unknown; however, few some common features role on etiology and pathogenesis to many soft tissue tumors:

  • Frequently, a history of antecedent trauma may bring the tumor to the attention of the patients.
  • Molecular and cytogenetic studies in many tumors reveal chromosomal abnormalities and mutations in genes which are used as a marker for diagnosis and histogenesis, for example, translocations, various fusions genes, etc.
  • Most commonly soft tissue tumors occur sporadically, few common examples are genetic syndrome like neurofibromatosis type I, Osler-Weber-Rendu syndrome, Li-Fraumeni syndrome, etc

Classification of soft tissue tumors

According to WHO, the tumors classified into the following four categories;

  1. Benign: generally do not recur and cured with the help of excision for example lipoma.
  2. Intermediate (locally aggressive): Don’t metastasize but locally destructive, infiltrative, and often recur and generally treated by wide excision for example desmoid tumor.
  3. Intermediate (rarely metastasizing): all characteristic features are similar to locally aggressive but around 2% of cases are clinically metastasis but not be predicted by morphology for example dermatofibrosarcoma protuberans.
  4. Malignant: locally destructive, infiltrative, and metastasized in a high percent of the cases. Low-grade sarcomas are about 2-10% however in high-grade sarcomas it is 20-100%.
Location Benign Malignant
Adipose tissue Lipoma Liposarcoma
Tumor and tumor-like lesions of fibrous tissue Nodular fasciitis, Fibromatoses (nodular fascitis), Superficial fibromatoses, Deep fibromatoses, fibroma fibrosarcoma
Fibrohistiocytic tumors

Fibrous histiocytoma

Dermatofibrosarcoma protuberans

Malignant fibrous histiocytoma
Skeletal muscle Rhabdomyoma Rhabdomyosarcoma
Smooth muscle Leiomyoma Leiomyosarcoma
Vascular tumors Hemangioma, Lymphangioma, Hemangioendothelioma Angiosarcoma
Peripheral nerve tumors Neurofibroma, Schwannoma, Granular cell tumor Malignant peripheral nerve sheath tumor
Tumors of uncertain histology   Synovial sarcoma, Alveolar soft part sarcoma, Epithelioid sarcoma, Granular cell tumor, clear cell sarcoma,
Classification of soft tissue tumors

Prognostic features of soft tissue tumors

  • Diagnostic classification
    • It is based on histology, electron microscopy, cytogenetics, immunohistochemistry, and molecular genetics features of the tumors.
  • Grading
    • According to the three grade systems such as grades I to III a low, intermediate, and high grades respectively, and grading is based on the degree of differentiation, an average number of mitoses per high-power field, pleomorphism, cellularity, and an estimate of the necrosis. 
  • Staging 
    • There are two most commonly accepted staging systems are Enneking’s staging and American Joint Committee (AJC)
      • > 20 cm tumor metastasis 80%
      • < 5 cm tumors metastasize 30%
  • Location 
    • Most commonly tumor arises superficial locations for example skin which have a better prognosis than deep-seated lesions of the soft tissue tumors.
    • Overall, the 10-year survival rate for sarcomas is normally around 40%

Does a soft tissue mass mean cancer?

Soft tissue tumors can be malignant (cancerous) or benign. Benign masses occur 10 times more frequently than malignant (cancerous) growths which are clinically called sarcomas. Generally, these growths are roughly round or oval in shape, but they also can be elliptical or elongated like a sausage.

Is soft tissue mass dangerous?

Most soft tissue tumors, mercifully, are made of adipose tissue (lipomas). They frequently occur just underneath the skin as a soft tissue mass, which is painless, This tumor grows slowly over months to years. These soft tissue tumors aren’t dangerous to the patient in general.

What are the symptoms of soft tissue cancer?

The symptoms of the soft tissue tumors are following;

  • The swelling extends or directly below the skin which may cause a painless lump that has an immovable mass and gets larger over time to time.
  • Swelling in the abdomen may cause abdominal pain, continuing feeling of fullness, and constipation(difficulty in emptying the bowels-stools).
  • Swelling around the lungs may cause a cough or breathlessness, difficulty in breathing.

What is the most common soft tissue tumor?

Liposarcoma is the most common soft tissue tumor, which originates in adipose tissue (fat cells) and is most commonly diagnosed in adults over the age of the 4th decade.

Tumors and tumorlike lesions of fibrous tissue

What is Fibromas?

It is an uncommon tumor but it is literally an example of hyperplastic fibrous tissue tumors. Three types of fibromas are identified in humans such as fibroma durum, fibroma molle (fibrolipoma), and elastofibroma.

Reactive tumors-like proliferations

  • Nodular fasciitis (pseudosarcomatous fasciitis)
  • Keloid
  • Myositis ossificans.

What is Keloid?

It is the progressive fibrous overgrowth in response to injuries such as incisions, burns, insect bites, vaccinations, and others.

Morphology of Keloid

  • Gross: smooth, firm, pink, raised patch (claw-like processes).
  • Microscopy: Homogenous materials, thick, eosinophilic hyalinised bands of collagen that mixed with thin collagenous fibers and large active fibroblasts.

What is Nodular fasciitis?

It is also called pseudosarcomatous fibromatosis. The common sites are the upper extremity, trunk, and neck region of young adults and it is generally cured by local excision however less than 5% of cases may have a local recurrence.

Morphology of Nodular fasciitis

  • Gross:
    • Solitary well-circumscribed nodule and size vary from cm to several cm in diameter.
  • Microscopy:
    • Whorled or S-shaped pattern of fibroblasts but individual cells are spindle-shaped, plump fibroblasts showing mild nuclear atypia with typical mitoses.

What is Myositis ossificans?

The misnomer benign, tumor-like lesion characterized by osteoid and heterotopic bone formation in the soft tissues.

Morphology of Myositis ossificans

  • Gross:
    • Unencapsulated, gritty mass replacing the muscle.
  • Microscopy:
    • Loosely arranged fibroblast with high mitotic activity. osteoid matrix formation

What is Fibromatosis?

It is actively proliferative tumors so difficult to differentiate from sarcomas, The myofibroblast cells are seen in the microscopy. Fibromatosis is broadly grouped they are infantile or juvenile fibromatoses and adult type of fibromatoses, they are;

  • Infantile or juvenile fibromatoses: 
    • Fibromatosis Colli
    • Juvenile aponeurotic fibroma
    • Fibrous hamartoma of infancy
    • Diffuse infantile fibromatosis
    • Juvenile nasopharyngeal angiofibroma
    • Congenital (generalized and solitary) fibromatosis.
  • Adult type of fibromatoses:
    • Palmar and plantar fibromatosis
    • Nodular fasciitis
    • Cicatricial fibromatosis
    • Keloid
    • Irradiation fibromatosis
    • Penile fibromatosis (Peyronie’s disease)
    • Abdominal and extra-abdominal desmoid fibromatosis
    • Retroperitoneal fibromatosis.

Palmar and plantar fibromatosis

  • It is also called Dupuytren-like contractures and most commonly occurs superficially.
  • Microscopy: Nodules are formed and composed of fibrovascular tissue having plump,  tightly packed fibroblast with high mitotic activity.

Desmoid (deep-seated) fibromatosis:

  • Gross:
    • Solitary, large, grey-white, firm, and un-encapsulated tumor infiltrating the muscle and cut section surface is whorled and trabeculated.
  • Microscopy:
    • Uniform fibroblasts arranged in bands and fascicles. Pleomorphism and mitosis are infrequent.






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