What is the diagnostic approach for muscle sarcoma?

Diagnostic Approach for Muscle Sarcoma

The standard diagnostic approach for muscle sarcoma consists of proper imaging followed by multiple core needle biopsies performed by a trained surgeon or radiologist, with all cases managed by a multidisciplinary team at a sarcoma reference center. 1

Initial Evaluation

• Any unexplained deep mass of soft tissues, superficial lesion >5 cm, or any soft tissue mass in pediatric patients should be referred to a sarcoma reference center 1
• MRI is the preferred imaging modality for extremity and trunk wall sarcomas, providing the most accurate information for diagnosis and surgical planning 1, 2
• CT scan is recommended for retroperitoneal tumors or as an alternative when MRI is not feasible 1
• Plain radiographs should be obtained first to rule out bone tumors, detect bone erosion, and identify calcifications 1

Imaging Protocol

• MRI with contrast enhancement is essential for proper assessment of soft tissue masses 1, 2
• CT angiogram may be useful in patients for whom MRI is not feasible 1
• For staging purposes, a chest CT scan is mandatory to exclude pulmonary metastases 1
• Abdominal/pelvic CT should be considered for specific histologic subtypes with high metastatic potential (myxoid liposarcoma, epithelioid sarcoma, angiosarcoma, leiomyosarcoma) 1
• MRI of the total spine should be considered for myxoid round cell liposarcomas due to higher risk for spine metastasis 1
• PET/CT may be useful for prognostication, grading, and assessing response to chemotherapy, though not yet established as routine 1

Biopsy Technique

• Multiple core needle biopsies using needles >16G are the standard approach for diagnosis 1
• Core biopsies should be performed under imaging guidance to avoid areas of necrosis 1, 2
• The biopsy should be planned so that the biopsy tract and scar can be safely removed during definitive surgery 1, 2
• An excisional biopsy may be appropriate for superficial lesions <5 cm 1
• Fine-needle aspiration is not recommended as a primary diagnostic modality outside centers with specific expertise 1, 2
• The biopsy entrance point should preferably be tattooed 1

Histopathological Assessment

• Histological diagnosis should be made according to the latest WHO classification 1, 2
• The malignancy grade should be provided using the FNCLCC system, which distinguishes three grades based on differentiation, necrosis, and mitotic rate 1
• Tumor samples should be fixed in formalin (avoid Bouin fixation as it prevents molecular analysis) 1
• Collection of fresh frozen tissue and tumor imprints is encouraged for potential future molecular analysis 1
• Pathological expert second opinion is recommended in all cases where the original diagnosis was made outside reference centers 1, 2

Molecular and Immunohistochemical Studies

• Immunohistochemistry is essential for accurate diagnosis of muscle sarcomas 3
• Molecular pathology (FISH, RT-PCR) should complement morphology and immunohistochemistry when 1:
  • The clinical-pathological presentation is unusual
  • The specific histological diagnosis is doubtful
  • It may have prognostic/predictive relevance

Common Pitfalls to Avoid

• Relying solely on ultrasound assessment without MRI can lead to misdiagnosis 2
• Performing excisional surgery without proper planning can result in inadequate margins requiring more extensive procedures later 4
• Frozen-section technique for immediate diagnosis is not encouraged as it generally does not allow a complete diagnosis 1
• Underestimating soft tissue masses as benign lesions without appropriate workup (soft tissue sarcomas are often confused with benign tumors, which are 100 times more common) 4
• Failure to refer patients with suspicious masses to specialized sarcoma centers 1

Staging and Risk Assessment

• Tumor size should be categorized as small (≤5 cm) or large (>5 cm) 1
• Tumor depth in relation to the muscular fascia (superficial vs. deep) should be recorded 1
• Histological grade is a critical prognostic factor 1
• The pathology report after definitive surgery should include a detailed description of tumor margins 1
• If preoperative treatment was carried out, the pathology report should include a tumor response assessment 1

By following this systematic diagnostic approach, clinicians can ensure accurate and timely diagnosis of muscle sarcomas, which is crucial for appropriate treatment planning and improved patient outcomes.