What is the best diagnostic method for soft tissue sarcoma?

Core Needle Biopsy is the Best Diagnostic Method for Soft Tissue Sarcoma

The standard approach to diagnosis of soft tissue sarcoma consists of multiple core needle biopsies using needles ≥16G, as this provides high diagnostic accuracy with minimal morbidity. 1

Diagnostic Algorithm for Soft Tissue Sarcoma

Initial Imaging (Before Biopsy)

• MRI is the main imaging modality for soft tissue tumors 1
• Standard radiographs should be performed first to:
  • Rule out bone tumor
  • Detect bone erosion with fracture risk
  • Identify calcifications 1
• CT has a role in:
  • Calcified lesions (to rule out myositis ossificans)
  • Retroperitoneal tumors 1

Biopsy Options

1. Core Needle Biopsy (CNB):

   • First-line choice for most suspected soft tissue sarcomas 1
   • Multiple cores using needles ≥16G
   • Accuracy for malignancy: 95-97.6% 2, 3
   • Accuracy for histologic subtype: 75-88% 3, 4
   • No complications reported in recent studies 2
   • Faster diagnosis (8.37 vs 15.63 days compared to incisional biopsy) 5

2. Excisional Biopsy:

   • Only recommended for superficial lesions <5 cm 1
   • Not appropriate for larger or deep lesions

3. Incisional Biopsy:

   • Option in selected cases where CNB is not feasible 1
   • Higher complication rates (wound infections, hematoma, pulmonary embolism) 2, 5
   • Similar accuracy to CNB but more invasive 5

4. Fine Needle Aspiration:

   • Not recommended except in centers with specific expertise 1

Important Considerations for Biopsy Procedure

• The biopsy should be performed by a trained surgeon or radiologist after interdisciplinary discussion 1
• Plan the biopsy pathway so that it can be safely removed during definitive surgery 1
• The biopsy entrance point should be tattooed 1
• Immediate evaluation of tissue viability may be considered to ensure adequate sampling 1
• Frozen-section technique for immediate diagnosis is not encouraged 1
• The tumor sample should be fixed in formalin (avoid Bouin fixation as it prevents molecular analysis) 1

Pathological Assessment

• Histological diagnosis should follow the WHO classification 1
• Malignancy grade should be provided using the FNCLCC grading system 1
• Core biopsy may underestimate tumor grade, so radiological imaging can help estimate malignancy grade 1
• Pathologic diagnosis relies on:
  • Morphology
  • Immunohistochemistry
  • Molecular pathology (FISH, RT-PCR) when needed 1

Pitfalls and Caveats

• CNB may underestimate tumor grade, particularly in low-grade sarcomas 6
• In 7-13% of cases, CNB specimens may be inadequate, requiring additional biopsy 3, 4
• A pathological expert second opinion is strongly recommended when diagnosis is made outside a reference center 1
• Collection of frozen tissue and tumor imprints is encouraged for potential future molecular assessments 1
• All patients with suspected sarcoma should be referred to specialized centers with multidisciplinary expertise 1, 7

Between options A (Incisional Biopsy) and C (Core Needle Biopsy), the evidence clearly supports Core Needle Biopsy (C) as the best diagnostic method for soft tissue sarcoma due to its high accuracy, minimal invasiveness, and fewer complications.