What is the diagnostic workup for soft tissue sarcoma (STS)?

From the Guidelines

The workup of a soft tissue sarcoma should start with an MRI with contrast of the affected area to define tumor extent and relationship to nearby structures, followed by a CT chest to evaluate for pulmonary metastases, as recommended by the most recent guidelines 1. The initial imaging assessment is crucial in determining the extent of the tumor and its relationship to surrounding structures.

• For most patients, a CT chest is essential to evaluate for pulmonary metastases, as lungs are the most common site of distant spread 1.
• However, for certain sarcoma subtypes with very low or negligible metastatic risk, such as atypical lipomatous tumours or classic dermatofibrosarcoma protuberans, a chest X-ray may be sufficient staging 1.
• Core needle biopsy is preferred over incisional biopsy for tissue diagnosis, ideally performed by an experienced radiologist or surgeon familiar with sarcoma management 1.
• The biopsy track should be planned carefully as it will need to be excised during definitive surgery.
• Laboratory studies including CBC, comprehensive metabolic panel, and LDH should be obtained.
• For certain histologic subtypes or anatomic locations, additional imaging may be warranted:
  • abdominal/pelvic CT for retroperitoneal sarcomas or myxoid liposarcoma 1
  • bone scan for potential osseous involvement
  • PET scan for high-grade tumors to detect occult metastases
  • contrast CT or MRI of the brain for alveolar soft part sarcoma and clear cell sarcoma due to a higher incidence of brain metastases 1
• Pathologic evaluation should include immunohistochemistry and molecular studies to determine specific sarcoma subtype, grade, and potential targetable mutations.
• Multidisciplinary tumor board discussion is crucial before initiating treatment, as management often involves coordination between surgical oncology, radiation oncology, and medical oncology 1.
• This comprehensive workup allows for accurate staging according to the AJCC system, which considers tumor size, depth, grade, nodal status, and presence of metastases, ultimately guiding treatment decisions.

From the Research

Workup of Soft Tissue Sarcoma

• The workup of soft tissue sarcoma involves a comprehensive approach, including imaging studies and histologic evaluation, to determine the extent of the disease and guide management decisions 2.
• Magnetic Resonance Imaging (MRI) is a fundamental tool in the evaluation of soft tissue sarcoma, providing information on tumor size, location, and prognostic features such as peritumoral enhancement, signs of necrosis, and deep location 3.
• The size of the mass is a key prognostic element in diagnostic imaging, with larger tumors generally associated with a poorer prognosis 3.
• Other MRI features, such as the "tail sign" in myxofibrosarcoma and undifferentiated pleomorphic sarcoma, and the "triple sign" in synovial sarcoma, can provide additional prognostic information 3.
• Signal heterogeneity on MRI is associated with a worse prognosis in all types of soft tissue sarcoma, particularly in myxoid liposarcoma 3.
• Radiomics, a quantitative tool applied to MRI, has been shown to predict patients' prognosis and discriminate between low-grade and high-grade soft tissue sarcomas 3.
• A treatment algorithm for soft tissue sarcoma should be based on a selective literature review and involve close interdisciplinary coordination between specialists in tumor orthopedics, oncology, radiology, pathology, and radiotherapy 4.
• The management of soft tissue sarcoma requires a histiotype-specific approach, with consideration of anatomic site, histology, and molecular characteristics 5.
• MRI has been shown to have high diagnostic accuracy for detecting recurrent soft tissue sarcoma, with a sensitivity of 92% and specificity of 98% in a long-term analysis at a multidisciplinary sarcoma center 6.

Diagnostic Imaging

• MRI is the preferred imaging modality for soft tissue sarcoma, providing detailed information on tumor extent and prognostic features 3, 6.
• Computed Tomography (CT) and Positron Emission Tomography (PET) may also be used in certain situations, such as evaluating distant metastases or assessing tumor response to treatment 2, 5.

Histologic Evaluation

• Histologic evaluation is critical in the diagnosis and management of soft tissue sarcoma, with over 100 different histologic subtypes recognized 2, 5.
• A comprehensive histologic evaluation should include immunohistochemistry, molecular diagnostics, and cytogenetic analysis to determine the specific subtype and guide management decisions 2, 5.