Indications for Sentinel Lymph Node Biopsy
Sentinel lymph node (SLN) biopsy is recommended for patients with intermediate-thickness melanomas (Breslow thickness 1-4 mm) of any anatomic site as it provides accurate staging and guides treatment decisions. 1
Primary Indications Based on Tumor Thickness
Intermediate-thickness melanomas (1-4 mm): SLN biopsy is strongly recommended for all patients with melanomas of Breslow thickness between 1-4 mm at any anatomic site. This provides accurate staging with high rates of successful mapping and acceptable false-negative rates. 1
Thick melanomas (>4 mm): SLN biopsy may be recommended for patients with thick melanomas (T4; Breslow thickness >4 mm) primarily for staging purposes and to facilitate regional disease control, despite fewer studies focusing specifically on this population. 1
Thin melanomas (<1 mm): There is insufficient evidence to support routine SLN biopsy for patients with thin melanomas (T1; Breslow thickness <1 mm). However, it may be considered in selected patients with high-risk features when the benefits of pathologic staging outweigh the potential risks of the procedure. 1
High-Risk Features in Thin Melanomas That May Warrant SLN Biopsy
For thin melanomas (<1 mm), SLN biopsy may be considered when the following high-risk features are present:
- Ulceration 1
- Mitotic rate ≥1/mm², especially in melanomas 0.75-0.99 mm in thickness 1
- Young patient age 2
- Clark level IV-V invasion 2
Clinical Significance and Purpose
SLN biopsy serves several important clinical purposes:
- Provides accurate nodal staging for patients at risk of clinically occult nodal metastases 1, 2
- Guides treatment decisions including completion lymph node dissection and adjuvant therapy 1
- Facilitates entry into clinical trials 1
- Achieves regional disease control with lower morbidity than complete lymph node dissection 2
Technical Considerations
- The procedure involves injection of radiocolloid (technetium sulfur colloid) and/or vital blue dye (isosulfan blue) around the primary tumor site 3, 4
- All blue-stained lymph nodes and nodes with ≥10% of the ex vivo radioactive count of the "hottest" node should be harvested for optimal detection of nodal metastases 4
- Intraoperative gamma probe detection improves the rate of SLN identification compared to blue dye alone 4
Management After Positive SLN Biopsy
- Completion lymph node dissection (CLND) is recommended for all patients with a positive SLN biopsy to achieve good regional disease control 1
- The impact of CLND on survival after a positive SLN biopsy was being evaluated in the Multicenter Selective Lymphadenectomy Trial II at the time of guideline publication 1
Contraindications and Cautions
- Patients with clinically positive lymph nodes or core biopsy-proven positive lymph nodes should undergo axillary lymph node dissection rather than SLN biopsy 5
- The safety of SLN biopsy in pregnant patients is not fully established 5
- Careful pathologic evaluation is essential, with attention to accurate reporting of the number and status of tumor-positive nodes 1
Evolving Applications
- SLN biopsy is being evaluated in other cancers beyond melanoma, including breast cancer and gastrointestinal malignancies 6, 7
- For breast cancer, SLN biopsy has become standard of care for early-stage disease with decreased morbidity compared to axillary lymph node dissection 5
SLN biopsy represents a significant advance in the staging and management of melanoma, providing critical prognostic information while minimizing surgical morbidity compared to complete lymphadenectomy. The procedure is most clearly indicated for intermediate-thickness melanomas, with conditional recommendations for thick melanomas and selected thin melanomas with high-risk features.