Classification of soft tissue sarcomas

Staging of soft tissue sarcomas

There is currently no generally accepted staging of childhood sarcomas. The two most commonly used classifications are the TNM classification of the International Union Against Cancer and the classification of the International Rhabdomyosarcoma Study Group.

Histological classification of soft tissue sarcomas

Histologically, soft tissue sarcomas are extremely heterogeneous. Below are presented variants of malignant sarcomas and the histogenetically corresponding tissue types.

Soft tissue sarcomas also include extraosseous tumors of bone and cartilage tissue (extraosseous osteosarcoma, myxoid and mesenchymal chondrosarcoma).

It is morphologically difficult to perform differential diagnostics between non-rhabdomyosarcoma soft tissue tumors. Electron microscopy, immunohistochemical and cytogenetic studies are used to clarify the diagnosis.

The histological type of a soft tissue tumor (except for rhabdomyosarcoma) does not provide a clear picture of the clinical course and prognosis of the disease. In order to determine the correlation between the histological type and tumor behavior, the multicenter research group POG (Pediatric Oncology Group, USA) in the course of a prospective study identified three types of histological changes that can be used as prognostic factors. The degree of histological changes was determined by the indices of cellularity, cellular pleomorphism, mitotic activity, severity of necrosis and invasive tumor growth. It was shown that tumors of the third group (grade III) have a significantly worse prognosis compared to the first and second.

Histological classification of soft tissue sarcomas

Fabrics	Types of tumors
Tumors of striated muscle tissue	Rhabdomyosarcoma
Tumors of smooth muscle tissue	Leiomyosarcoma
Tumors of fibrous tissue	Infantile fibrosarcoma
	Dermatofibrosarcoma
Fibrohistiocytic tumors	Malignant fibrocytic histiocytoma
Tumors of adipose tissue	Liposarcoma
Vascular tumors	Angiosarcoma
	Lymphangiosarcoma
	Hemangiopericytoma malignant
	Hemangioendothelioma
	Kaposi's sarcoma
Peripheral nerve sheath tumors	Malignant schwannoma
Tumors of various histogenesis	Malignant mesenchymoma
	Triton tumor
Tumors of unknown histogenesis	Synovial sarcoma
	Epithelioid sarcoma
	Alveolar soft tissue sarcoma
	Malignant melanoma of soft tissue
	Desmoplastic small round cell sarcoma

Degree I.

• Myxoid and well-differentiated liposarcoma.
• Deep seated dermatofibrosarcoma.
• Well differentiated or infantile fibrosarcoma.
• Well differentiated hemangiopericytoma.
• Well differentiated malignant tumor of the peripheral nerve sheaths.
• Extraosseous myxoid chondrosarcoma.
• Malignant fibrocytic histiocytoma.

Degree II.

• Soft tissue sarcomas not included in the first and third groups. Signs of necrosis are found on less than 15% of the tumor surface, microscopy with x40 magnification reveals less than five mitotic figures in 10 fields of view, no atypia of cell nuclei, low cellularity.

Degree III.

• Pleomorphic or round cell liposarcoma.
• Mesenchymal chondrosarcoma.
• Extraosseous osteosarcoma.
• Triton tumor.
• Alveolar sarcoma of soft tissue.
• Synovial sarcoma.
• Epithelioid sarcoma.
• Clear cell sarcoma of soft tissue (malignant melanoma of soft tissue).
• Soft tissue sarcomas not included in the first group, having signs of necrosis on more than 15% of the surface or more than 5 mitotic figures when examined microscopically with a magnification of x40.

TNM classification

Primary tumor.

• T ₁ - the tumor is limited to the organ (tissue) from which it originates.
• T ₂ - the tumor extends beyond the organ (tissue).
  • T _2a - the tumor diameter is less than or equal to 5 cm.
  • T _2b - the tumor is more than 5 cm in diameter.
• Regional lymph nodes.
  • N ₀ - regional lymph nodes are not affected.
  • N ₁ - damage to regional lymph nodes.
  • N _x - insufficient data to assess lymph node involvement.
• Distant metastases.
  • M ₀ - no distant metastases.
  • M ₁ - there are distant metastases.

The prognostic significance of TNM factors has been demonstrated in a number of studies on soft tissue sarcomas in children.

The International Rhabdomyosarcoma Study Group classification of soft tissue sarcomas , originally developed for rhabdomyosarcoma, is now used for all soft tissue tumors. It takes into account the volume of residual tumor after surgery and the presence of metastases.

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