Do lymph nodes need to be sampled in a patient with melanoma (malignant melanoma) on their back?

Sentinel Lymph Node Biopsy for Back Melanoma

Lymph nodes should be sampled via sentinel lymph node biopsy (SLNB) for melanomas ≥1.0 mm Breslow thickness on the back, as this is the most important prognostic factor and provides critical staging information that guides treatment decisions. 1, 2

When SLNB is Indicated

For melanomas ≥1.0 mm thickness:

• SLNB is the standard recommended procedure for all melanomas 1.0 mm or thicker 1
• Approximately 20% of these patients will have a positive sentinel node 1
• The procedure should only be performed by skilled teams in experienced centers 1

For melanomas 0.75-0.99 mm thickness:

• SLNB can be considered, particularly if the melanoma has high-risk features 3
• High-risk features include: ulceration (T1b), Clark level IV/V, mitotic rate ≥1 mitosis/mm², or younger age (≤40 years) 3
• Even thin melanomas (<1.0 mm) carry a 5% risk of positive SLNB 1

For melanomas <0.75 mm thickness:

• SLNB is generally not recommended unless multiple high-risk features are present 3

Critical Pre-Procedure Requirements

Before performing SLNB, you must:

• Confirm the diagnosis with full-thickness excisional biopsy showing Breslow thickness, ulceration status, and mitotic rate 1, 4
• Perform SLNB at the same time as definitive wide excision of the primary melanoma 1
• Use preoperative lymphoscintigraphy for trunk melanomas (like back melanomas) to accurately identify drainage basins 5
• Note that back melanomas may drain to unexpected or multiple nodal basins, making lymphoscintigraphy particularly important 5

Prognostic Significance

SLNB status is the most powerful prognostic indicator:

• Patients with negative SLNB have 90-97.9% 5-year survival 1, 2
• Patients with positive SLNB have 75% 5-year survival 1
• The number of positive sentinel nodes is the most powerful predictor of overall and disease-free survival 2

What Happens After SLNB

If SLNB is positive:

• Approximately 20% will have additional metastases in regional nodes 1
• Most patients proceed to completion lymphadenectomy, though this decision should be discussed 1
• Histologic confirmation via fine needle aspiration or open biopsy is recommended before formal block dissection 1

If SLNB is negative:

• No further nodal surgery is needed 1
• Routine elective lymphadenectomy is not recommended 1

Important Caveats

Technical considerations:

• The procedure carries 5% morbidity, significantly less than complete nodal dissection 1
• In approximately 5% of cases, the sentinel node cannot be identified 1
• Multiple sections with both H&E and immunohistochemical staining (S-100, HMB-45) are required for accurate pathologic examination 6

Imaging is NOT a substitute:

• Routine PET/CT scanning is not recommended for clinically localized melanoma and has very low yield 1, 7
• Cross-sectional imaging should not be used for initial staging of stage I-II melanoma 1
• PET/CT may be considered only for stage IIB-IIC or higher to evaluate for distant metastases 1