What are the indications for dynamic sentinel lymph node (SLN) biopsy in carcinoma of the penis?

Indications of Dynamic Sentinel Lymph Node Biopsy in Carcinoma Penis

Dynamic sentinel lymph node biopsy (DSNB) is primarily indicated in patients with penile carcinoma who have non-palpable inguinal lymph nodes (cN0) and intermediate (T1G2) or high-risk (T1G3 or worse) disease. 1

Patient Selection for DSNB

Risk Stratification

• Low-risk patients (pTa, pTis, pT1a G1):

  • DSNB not indicated due to very low risk of lymph node metastasis
  • Surveillance is recommended 1

• Intermediate-risk patients:

  • pT1a G2: 6-8% risk of micrometastatic disease 1
  • DSNB may be considered on a case-by-case basis, balancing risk of metastasis against surgical morbidity

• High-risk patients:

  • pT1b G2: 22-30% risk of lymph node metastasis 1
  • pT1b G3 or worse (T2-T3): DSNB strongly indicated
  • Early detection of lymph node metastases by DSNB in these patients improves survival compared to surveillance 1

Clinical Scenarios

Non-palpable Lymph Nodes (cN0)

DSNB is indicated when:

• Physical examination reveals non-palpable inguinal nodes
• Patient has intermediate or high-risk primary tumor characteristics
• No evidence of distant metastases on imaging

Palpable Lymph Nodes (cN+)

• DSNB is NOT indicated
• Fine-needle aspiration cytology (FNAC) is recommended instead 1
• If FNAC is positive: proceed to inguinal lymph node dissection (ILND)
• If FNAC is negative but clinical suspicion remains: repeat biopsy or node excision 1

Technical Considerations

DSNB involves:

1. Preoperative lymphoscintigraphy with 99mTc-nanocolloid injected intradermally around the tumor
2. Intraoperative identification using patent blue dye and gamma detection probe
3. Excision of identified sentinel nodes
4. Histopathological examination of removed nodes
5. Completion ILND if sentinel node is positive for metastasis 2, 3

Efficacy and Performance Metrics

DSNB demonstrates:

• Sentinel node identification rate: 97% 1
• Pooled detection rate: 88.3% 1
• Pooled sensitivity: 88.0% 1
• False-negative rate: 7% 1
• Complication rate: 4.7% 1

A recent meta-analysis of DSNB in 2023 showed:

• Pooled weighted sensitivity: 0.87 (95% CI: 0.82-0.91) 4
• However, positive DSNB has limited ability to predict which patients will have further metastatic involvement at completion ILND 4

Advantages of DSNB over Other Approaches

1. Lower morbidity: DSNB is less invasive compared to prophylactic ILND 1
2. Individualized approach: Based on mapping of individual lymphatic drainage patterns 2
3. High accuracy: Especially in high-volume centers (sensitivity 92-96%) 1
4. Improved survival: Early detection and treatment of occult metastases improves outcomes 1

Alternative Approaches When DSNB Not Available

If DSNB is not available, alternative approaches include:

• Ultrasound-guided FNAC of visualized nodes 1
• Risk factor assessment and nomograms 1
• Modified or minimally invasive ILND techniques 1

Potential Pitfalls and Limitations

• Requires specialized expertise and equipment
• Learning curve affects accuracy (best results in high-volume centers)
• False-negative results can occur (3.1-3.5%) 5
• Not widely available in all centers 1
• Requires careful patient selection to maximize benefit

DSNB represents an important advancement in the management of penile cancer, allowing for accurate staging with minimal morbidity when performed in appropriate patients by experienced centers.