Soft tissue tumor prognosis is characterized by a wide variability, ranging from neoplasms completely indolent to those very aggressive. The biological behavior is classified by the WHO into three categories: benign, intermediate (including forms that can locally recur and those at low risk of metastasis), and malignant (which are characterized by high risk of metastasis). Of note, some subtypes of soft tissue tumors classified among benign neoplasms can actually behave as tumors of intermediate malignant potential (e.g., cellular and atypical variants of benign fibrous histiocytoma).

Considering benign soft tissue tumors, the overall prognosis is excellent. However, some of these neoplasms can be life-threatening because of their complications (e.g., Kasabach-Merritt syndrome in giant hemangiomas, retroperitoneal hemorrhage from renal angiomyolipoma).

Soft tissue tumors with intermediate malignant potential include forms that can locally recur and those at low risk of metastasis, while malignant soft tissue tumors are characterized by high risk of metastasis.

The term “sarcoma” is used for tumors with both intermediate and malignant behavior.

As regards soft tissue sarcomas, some of them may be accompanied by metastasis at presentation, the prognosis being usually dismal. Among patients without metastatic disease at presentation, about 25% will develop distant metastatic disease (after undergoing radical surgery for their primary tumor), a proportion that increases up to 50% in cases with large (>5 cm), deep-seated (underneath the fascia), intermediate-/high-grade tumors.

The lungs are the most frequent site of distant metastasis (up to 80%). Some sarcomas are characterized by metastatic spread also to other sites such as the abdomen (e.g., round cell/myxoid liposarcoma, angiosarcoma, epithelioid sarcoma, and leiomyosarcoma), brain (e.g., angiosarcoma, alveolar soft part sarcoma, and clear cell sarcoma), and spine (spine bones and paraspinal tissues; e.g., round cell/myxoid liposarcoma). Finally, soft tissue sarcomas (unlike carcinomas) rarely involve lymph nodes, though with some exception, such as rhabdomyosarcoma (10–30%), synovial sarcoma (10–20%), clear cell sarcoma (15–40%), epithelioid sarcoma (10–30%), angiosarcoma (5–10%), leiomyosarcoma (3%), and malignant peripheral nerve sheath tumor (3%).

Patient survival depends upon tumor aggressiveness, disease stage, and responsiveness to treatment: therefore, prognosis of patients with sarcoma greatly varies across different tumor types. Overall, median overall survival of patients with metastatic sarcoma is approximately 16 months. In the USA, it is estimated that approximately 5000 deaths are due to soft tissue sarcomas each year.

Soft tissue sarcoma prognosis is stratified based on the American Joint Committee on Cancer (AJCC)/Union for International Cancer Control (UICC) TNM staging system. Four separate TNM staging systems have been generated based on tumor anatomic location: (a) TNM for soft tissue sarcomas of the head and neck (→ see Table 6.1); (b) TNM for soft tissue sarcomas of the trunk and extremities (→ see Tables 6.2 and 6.3); (c) TNM for soft tissue sarcomas of the abdomen and thoracic visceral organs (→ see Table 6.4); and (d) TNM for soft tissue sarcomas of the retroperitoneum (→ see Tables 6.5 and 6.6). According to the latest TNM version (eighth edition, published in 2017), the notation about the depth of the tumor (above or below the muscular fascia)—which was previously associated with a worse prognosis in case of deep location—has been eliminated.

Table 6.1 TNM staging for soft tissue sarcomas of head and necka
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Table 6.2 TNM staging for soft tissue sarcomas of trunk and extremities
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Table 6.3 TNM stages for soft tissue sarcomas of trunk and extremities
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Table 6.4 TNM staging for soft tissue sarcomas of the abdomen and thoracic visceral organsa
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Table 6.5 TNM staging for soft tissue sarcomas of the retroperitoneum
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Table 6.6 TNM stages for soft tissue sarcomas of the retroperitoneum
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Separate TNM staging systems have been proposed for specific soft tissue sarcomas, such as rhabdomyosarcoma and gastrointestinal stromal tumor/GIST (for details → see sections dedicated to rhabdomyosarcoma and GIST in the second part of the book).

Unlike other cancers, the TNM system for soft tissue sarcomas is characterized by the inclusion of histological grading (also known as tumor grade, G), which adopts the system proposed by the Fédération Nationale des Centres de Lutte Contre Le Cancer (French Federation of Cancer Centers, FNCLCC) (→ see Table 6.7). For some soft tissue sarcomas, tumor grade is directly assigned based on the histological type (→ see Table 6.8). This parameter is more associated with the risk of distant metastasis and death rather than with local disease recurrence (which is mainly dictated by histological type and surgical margins); importantly, tumor grading is not recommended for the following sarcomas: malignant peripheral nerve sheath tumor, embryonal rhabdomyosarcoma, alveolar rhabdomyosarcoma, angiosarcoma, extraskeletal myxoid chondrosarcoma, alveolar soft part sarcoma, clear cell sarcoma, and epithelioid sarcoma. Of note, grading cannot be assigned after neoadjuvant (i.e., preoperative) medical treatment.

Table 6.7 Histological grading of soft tissue sarcomas (FNCLCC system)
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Table 6.8 Tumor differentiation score by histologic type
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Finally, other tumor grading systems (e.g., the US National Cancer Institute grading system) have been devised and are variably utilized.