1. Introduction
Soft tissue sarcomas are rare tumours arising from mesenchymal tissues, representing approximately 1% of all adult malignancies. They are an extremely heterogenous group of tumours, composed of over 50 subtypes with distinct pathologic features and clinical behaviours. The commonest subtypes are liposarcoma, leiomyosarcoma, synovial sarcoma, malignant peripheral nerve sheath tumour and undifferentiated pleomorphic sarcomas. The majority of soft tissue sarcomas arise in the extremities and trunk (80%), with 15% arising in the retroperitoneum. Soft tissue sarcomas preferentially metastasize to the lungs (90%), and regional lymph nodes (5%).
2. Prevention
Not applicable to soft tissue sarcoma.
3. Screening and Early Detection
Not applicable to soft tissue sarcoma.
4. Diagnosis
All patients with soft tissue sarcoma should be assessed in a multidisciplinary clinic with expertise in sarcoma. Local imaging of the primary tumour must include MRI for extremity and trunk locations and MRI with CT for retroperitoneal tumours. Chest CT must be done on all patients. Other staging studies are indicated for specific subtypes – Abdominal/pelvic CT for myxoid/round cell liposarcoma; CT imaging of regional lymph nodes for epithelioid sarcoma, clear cell sarcoma, angiosarcoma and rhabdomyosarcoma and synovial sarcoma.
Important staging information to be gained from imaging of the primary site includes the maximal tumour diameter (< or > 5 cm) and the relationship to the superficial fascia (deep or superficial). Other information pertinent to local treatment planning includes involvement of major vascular structures, major motor nerves, bone and pelvic/abdominal organs.
Tissue diagnosis must be obtained by core needle or open incisional biopsy. If open biopsy is undertaken, the incision must be longitudinal in the extremities and in line with the eventual definitive resection incision, with minimal contamination of the surrounding tissues. The crucial information from biopsy includes tumour grade (low, medium and high grade) and sarcoma subtype.
Staging is carried out according to the AJCC staging system, which considers the factors of tumour size and location, grade, lymph node involvement and distant metastases:
5. Pathology
All sarcoma biopsies and resection specimens should undergo pathologic assessment by an experienced sarcoma pathologist. Biopsies should establish a malignant diagnosis, sarcoma subtype and grade. Ancillary tests such as immunohistochemistry, EM, cytogenetics and molecular genetic testing may be used in addition to morphologic assessment to establish a diagnosis, so assessment should be carried out in a site with access to the ancillary techniques.
The pathology synoptic report should contain the following information: tumour location, primary diagnosis (WHO classification), depth (superficial or deep), size, histologic grade (using FNCLCC or NCIC classifications), necrosis, status of margins, status of lymph nodes, results of ancillary tests, additional features if present (mitoses, vascular invasion, character of tumour margin) and TNM stage.
Although morphologic examination is the gold standard for most sarcoma diagnoses, molecular genetic testing has emerged as an important ancillary technique as many sarcomas feature typical and characteristic genetic abnormalities. Sarcomas whose diagnosis are confirmed using genetic testing using FISH or PCR include: Ewing’s sarcoma, desmoplastic small round cell tumour, alveolar rhabdomyosarcoma, myxoid/round cell liposarcoma, atypical lipomatous tumour, dedifferentiated liposarcoma, alveolar soft part sarcoma, clear cell sarcoma, dermatofibrosarcoma protuberans, extraskeletal myxoid chondrosarcoma, fibromyxoid sarcoma and synovial sarcoma,