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)?

Core Needle Biopsy is the Recommended Next Step for a 5 cm Triceps Mass

Core needle biopsy (CNB) is the most appropriate next step for this 45-year-old patient with a 5 cm mass originating from the triceps as shown on MRI. 1

Rationale for Core Needle Biopsy

Core needle biopsy is recommended as the first-line diagnostic procedure for deep soft tissue masses like this one for several key reasons:

• It provides an optimal balance between diagnostic accuracy and minimal patient morbidity
• High diagnostic accuracy: 97% sensitivity and 99% specificity for determining malignancy
• 88% accuracy for determining histologic subtype 1
• Can be performed as an outpatient procedure with local anesthesia, significantly reducing costs and patient inconvenience 2

Why Other Options Are Not Preferred

Incisional Biopsy

• Causes unnecessary contamination of tissue compartments
• Higher morbidity compared to CNB
• Similar diagnostic accuracy to properly performed CNB 1
• Substantially higher cost (approximately $7,234 compared to $1,106 for CNB) 2

Excisional Biopsy

• Specifically contraindicated for potentially malignant lesions of this size (5 cm)
• Should only be considered for superficial lesions <5 cm 1
• May compromise future definitive treatment if the mass proves malignant

PET Scan

• Not indicated as the next step before histological diagnosis
• May be useful for staging after histological confirmation of malignancy, but not for initial diagnosis

Technical Considerations for CNB

For optimal results, the core needle biopsy should:

• Use needles ≥16G to ensure adequate tissue sampling 1
• Be performed at a reference center by:
  • The surgeon who will perform definitive resection, or
  • A radiologist with expertise in musculoskeletal tumors 1
• Be planned so the biopsy tract can be safely removed during definitive surgery
• Include tattooing of the biopsy entrance point for future identification 1

Diagnostic Accuracy and Potential Limitations

While CNB is highly accurate, clinicians should be aware of potential limitations:

• Approximately 13% of CNBs may yield no neoplastic tissue 2
• CNB may occasionally underestimate tumor malignancy grade 1
• Diagnostic challenges can occur with myxomatous masses 2
• Overall accuracy ranges from 77-84%, with higher accuracy for bone lesions (85-96%) than soft tissue lesions (68-78%) 2, 3

Multidisciplinary Approach

The European Society for Medical Oncology (ESMO) emphasizes that:

• Diagnosis should be conducted within a multidisciplinary team at reference centers for sarcomas
• Team should include pathologists, radiologists, surgeons, radiation therapists, and medical oncologists
• Pathological expert second opinion is strongly recommended when diagnosis is made outside a reference center 1

In conclusion, core needle biopsy represents the most appropriate next step for this patient, providing the best balance of diagnostic accuracy, safety, and preservation of treatment options while avoiding unnecessary morbidity.