Soft tissue tumors

• Soft tissue


  Non-epithelial tissue other than bone, cartilage, CNS, hematopoietic, and lymphoid tissues
• Benign soft tissue tumors outnumber their malignant counterparts by at least 100 : 1
• Soft tissue tumours are classified according to the tissue type they recapitulate

  • Fat
  • Fibrous tissue
  • Neurovascular tissue
  • Muscular tissue

  
• Pathogenesis of soft tissue sarcomas

  • Most are sporadic and have no known predisposing cause
  • A small minority are associated with germline mutations in tumor suppressor genes
  • A few can be linked to known environmental exposures such as radiation, burns, or toxins

  
• Site


  Soft tissue tumors can arise in any location, although approximately 40% occur in the lower extremities, especially the thigh

  
• Age


  • The incidence generally increases with age, although 15% arise in children
  • Certain sarcomas tend to appear in certain age groups (Rhabdomyosarcoma in children, Synovial sarcoma in young adulthood, Liposarcoma and undifferentiated pleomorphic sarcoma in later adult life)
• Tumors of Adipose Tissue

  • Lipomas
  • Liposarcoma

  
• Fibrous Tissue


  • Nodular fasciitis
  • Superficial fibromatoses
  • Deep fibromatoses

  
• Tumors of Skeletal Muscle

  • Rhabdomyoma
  • Rhabdomyosarcoma

  
• Tumors of Uncertain Histogenesis

  • Synovial sarcoma
  • Undifferentiated pleomorphic sarcoma

  
• Lipomas


  Benign tumors of the fat cells (adipocytes), the most common soft tissue tumors of adulthood, complete excision is usually curative, common occurrence sites are fat depositing areas like neck, back and shoulder

  
• Lipoma Morphology


  • Usually round or oval in shape with variable size, freely movable and not attached to the skin or deeper tissues, capsulated, grows very slowly, histologically consist of mature white fat cells with no pleomorphism

  
• Liposarcoma


  Malignant neoplasms of adipocytes, most arise in the deep soft tissues and retroperitoneum, prognosis influenced by histologic subtype (well-differentiated types have more favorable outlook than aggressive poorly differentiated tumors), metastasize to lungs

  
• Liposarcoma Morphology


  • Large relatively well-circumscribed lesions, soft tissue mass that is soft, yellow, lobulated, with marked areas of hemorrhage and necrosis

  
• Liposarcoma Subtypes


  • Well-differentiated liposarcoma
  • Myxoid liposarcoma
  • Pleomorphic liposarcoma

  
• Nodular fasciitis


  Self-limited fibroblastic and myofibroblastic proliferation that typically occurs in the upper extremities of young adults, often with a history of trauma, can spontaneously regress and rarely recurs

  
• Nodular fasciitis Morphology


  • Several centimetres in greatest dimension, nodular with poorly defined margins, richly cellular with plump, randomly arranged, immature-appearing fibroblasts in an abundant myxoid stroma

  
• Fibromatoses


  Fibroblastic proliferations that grow in an infiltrative fashion and recur after surgical removal, although some are locally aggressive they do not metastasize, divided into superficial and deep types
• Fibromatoses Morphology


  • Gray-white, firm to rubbery, poorly demarcated, infiltrative masses 1 to 15 cm in greatest dimension, composed of plump fibroblastic cells arranged in broad sweeping fascicles that penetrate the adjacent tissue

  
• Rhabdomyosarcoma


  Malignant mesenchymal tumor with skeletal muscle differentiation, the most common soft tissue sarcoma of childhood and adolescence, often arises in the sinuses, head and neck, and genitourinary tract locations

  
• Rhabdomyosarcoma Subtypes


  • Embryonal
  • Alveolar
  • Pleomorphic
• Rhabdomyosarcoma Morphology


  • Variable gross appearance, can present as soft, gelatinous, grapelike masses (sarcoma botryoides) or as poorly defined, infiltrating masses
  • Embryonal: sheets of primitive round and spindled cells, may contain rhabdomyoblasts
  • Alveolar: network of fibrous septae dividing cells into clusters
  • Pleomorphic: numerous large, sometimes multinucleated, bizarre eosinophilic tumor cells
• Synovial Sarcoma


  Accounts for approximately 10% of all soft tissue sarcomas, most develop in deep soft tissues around the large joints of the extremities, common sites of metastasis are the lung and regional lymph nodes
• Synovial Sarcoma Morphology


  • Biphasic: exhibits differentiation of tumor cells into both epithelial-like cells and spindle cells
  • Monophasic: composed of spindled cells or, rarely, epithelial cells only
• Undifferentiated Pleomorphic Sarcoma


  Malignant mesenchymal tumors with high-grade, pleomorphic cells that cannot be classified into another category, most arise in the deep soft tissues of the extremity, especially the thigh of middle aged or older adults
• Undifferentiated Pleomorphic Sarcoma Morphology

  • Sheets of large, anaplastic, spindled to polygonal cells with hyperchromatic irregular, sometimes bizarre nuclei, abundant mitotic figures and necrosis
• Embryonal rhabdomyosarcoma:

  consist of sheets of both primitive round and spindled cells. Rhabdomyoblasts with visible cross-striations may be present
• Alveolar rhabdomyosarcoma:

  a network of fibrous septae divide the cells into clusters or aggregates, creating a crude resemblance to pulmonary alveoli.
• Pleomorphic rhabdomyosarcoma

  is characterized by numerous large, sometimes multinucleated, bizarre eosinophilic tumor cells that can resemble other pleomorphic sarcomas. Immunohistochemical identification of

  muscle specific proteins such as myogenin is usually necessary to confirm rhabdomyoblastic differentiation.
• superficial fibromatoses:

  arise in the superficial fascia and include such entities as palmar, Plantar and penile fibromatosis. They come to clinical attention early, because they cause deformity of the involved structure.
• deep fibromatoses (desmoid tumours)

  arise in the musculoaponeurotic structures of the anterior abdominal wall, extremities and within the abdomen (mesentery and pelvic walls). Deep fibromatoses tend to grow in a locally aggressive manner and recur after excision.