What is the next step in managing a 45-year-old patient with a 5 cm mass in the right upper limb, originating from the triceps, as shown on Magnetic Resonance Imaging (MRI)?

Management of a 5 cm Triceps Mass in the Right Upper Limb

Core needle biopsy (CNB) is the recommended next step for a 45-year-old patient with a 5 cm mass in the right upper limb originating from the triceps as shown on MRI. 1, 2

Rationale for Core Needle Biopsy

• Core needle biopsy represents the standard diagnostic approach for suspected soft tissue sarcomas, offering an optimal balance between diagnostic accuracy and minimal patient morbidity 2
• For deep soft tissue masses like this triceps lesion, CNB is specifically recommended by ESMO guidelines as the first-line diagnostic procedure 1
• The procedure should use needles ≥16G to ensure adequate tissue sampling 1, 2

Why CNB is Superior to Other Options

1. Compared to incisional biopsy (option A):

   • CNB is less invasive with lower complication rates (1% vs higher for open procedures) 3
   • Avoids unnecessary contamination of tissue compartments 1
   • Provides comparable diagnostic accuracy when performed properly 4

2. Compared to excisional biopsy (option B):

   • Excisional biopsy is contraindicated for potentially malignant lesions of this size 1
   • ESMO guidelines specifically state that excisional biopsy should only be considered for superficial lesions <5 cm 1
   • This 5 cm triceps mass is deep-seated and requires proper diagnostic workup before definitive treatment

3. Compared to PET scan (option D):

   • Tissue diagnosis must precede advanced imaging for treatment planning 1
   • PET scan may be useful for staging after histological confirmation, not as a diagnostic tool 1

Important Technical Considerations

• The biopsy should be performed at a reference center by a surgeon who will perform the definitive resection or by a radiologist with expertise in musculoskeletal tumors 1
• CT guidance may be beneficial for deep-seated lesions to improve targeting accuracy 5
• The biopsy pathway should be planned so it can be safely removed during definitive surgery 1, 2
• The biopsy entrance point should be tattooed for future identification 1

Diagnostic Accuracy of CNB

• Studies show CNB has a diagnostic yield of 84.7-93% for musculoskeletal lesions 3, 6
• Accuracy rates of 91.7-97% for determining malignancy 3, 4
• 88% accuracy for determining histologic grade, which is critical for treatment planning 4

Common Pitfalls to Avoid

• Inadequate sampling: Ensure multiple cores are obtained to minimize sampling error 2
• Improper handling of specimens: Tissue should be fixed in formalin (avoid Bouin fixation which prevents molecular analysis) 1
• Interpretation by inexperienced pathologists: Samples should be evaluated by pathologists with expertise in musculoskeletal tumors 1, 2
• Poor biopsy planning: The biopsy tract must be considered contaminated and should be excised during definitive surgery 1

Core needle biopsy provides the optimal balance of diagnostic accuracy and safety for this patient's presentation, allowing for proper treatment planning while minimizing morbidity.