What is Sentinel Lymph Node Biopsy (SLNB) for?

What is Sentinel Lymph Node Biopsy (SLNB) For?

Sentinel lymph node biopsy is a minimally invasive surgical staging procedure that identifies and removes the first lymph node(s) to receive drainage from a tumor, allowing accurate assessment of lymph node metastasis while avoiding the morbidity of complete lymph node dissection in patients who are node-negative. 1, 2

Primary Indications

Breast Cancer

SLNB is the standard of care for axillary staging in clinically node-negative early-stage breast cancer (T1-T2, stages I-II) undergoing upfront surgery. 3, 1 This applies to:

• Patients with invasive breast cancer ≤5 cm with clinically negative axillary nodes confirmed by physical examination and negative preoperative axillary ultrasound 1
• Both breast-conserving surgery and mastectomy candidates 1
• SLNB has replaced routine axillary lymph node dissection (ALND) as the standard staging procedure 3, 2

Melanoma

SLNB is recommended for intermediate-thickness melanomas (1-4 mm Breslow thickness) and should be discussed for stage IA thin melanomas (≤1.0 mm) with adverse features. 3, 1 Specific indications include:

• Stage IB or II melanoma (>1.0 mm thick or ≤1.0 mm with ulceration/Clark level IV-V) 3, 1
• Thin melanomas >0.75 mm with high mitotic rate, young age, positive deep margins, or lymphovascular invasion 1

Other Malignancies

SLNB is standard of care for early-stage cervical cancer (FIGO stage IA2, IB, IIA) and vulvar cancer when performed at centers with adequate expertise. 2

Core Clinical Purposes

Accurate Staging with Minimal Morbidity

SLNB provides enhanced staging accuracy by allowing pathologists to perform comprehensive examination of the 1-2 nodes most likely to contain metastases, rather than superficial examination of 10-20 nodes from complete dissection. 2 The procedure achieves:

• Identification rates >95% when performed by experienced surgeons 3
• False-negative rates <10% with proper technique 1, 2
• Significantly lower morbidity than complete lymph node dissection with equivalent survival outcomes 2

Guiding Treatment Decisions

Nodal status determined by SLNB remains the most significant prognostic factor and directly guides multiple treatment decisions: 3, 2

• Selection of candidates for adjuvant systemic therapy based on nodal status 2
• Determination of need for completion lymph node dissection when sentinel nodes are positive 2
• Radiation therapy planning, particularly when unexpected drainage patterns are identified 2
• Entry criteria for clinical trials evaluating new adjuvant therapies 2

Avoiding Unnecessary Surgery

SLNB spares 75-80% of patients who have tumor-free sentinel nodes from unnecessary complete dissection and its associated complications. 2 This includes avoiding:

• Lymphedema (chronic arm swelling) 3
• Nerve injury and shoulder dysfunction 3, 4
• Other complications that compromise functionality and quality of life 3

Technical Requirements for Accuracy

SLNB should only be performed by surgeons with demonstrated false-negative rates <10% and successful mapping rates >90%. 1 Critical technical elements include:

• Dual technique using both radiotracer and blue dye achieves the highest success rates and lowest false-negative rates 1
• Surgeons must demonstrate competency by performing 20-30 sentinel node biopsies with completion dissection before abandoning routine complete dissection 2
• Pathologic processing requires slicing nodes no thicker than 2.0 mm and examining at least one section from each block 2

Management Based on SLNB Results

Negative SLNB

Appropriately identified patients with negative SLNB do not require completion ALND. 3 The axillary recurrence rate in SLNB-negative patients is 0-1.6%, comparable to the 0-3% rate after ALND. 5

Positive SLNB

Completion lymph node dissection has traditionally been recommended for all patients with positive SLNB. 3 However, recent evidence suggests observation may be appropriate for low-burden disease in selected breast cancer patients. 2

Special Circumstances and Contraindications

Neoadjuvant Chemotherapy

SLNB may be offered before or after neoadjuvant chemotherapy (NACT), but the false-negative rate is higher afterward (10-30%), making the procedure less accurate after NACT. 3 Key considerations:

• SLNB is not recommended in patients with T4d/inflammatory breast cancer who have received NACT 3
• For patients with metastatic nodes before NACT, the high false-negative rate after treatment may result in understaging and undertreatment 3
• At least two SLNs should be removed after NACT to minimize false-negative rates 3

When SLNB Should Not Be Performed

Clinical examination alone is not sufficient—ultrasound should be used to identify occult nodal disease in clinically node-negative patients. 1 SLNB is unlikely to be appropriate for:

• Large tumors and locally advanced invasive tumors 3
• Patients with suspicious palpable axillary nodes 3
• Before neoadjuvant therapy, as this compromises the ability to assess treatment response 1

Pathologic Evaluation Considerations

The role of routine immunohistochemistry (IHC) for detection of isolated tumor cells or micrometastases remains unclear. 3 Evidence shows:

• Neither the NSABP B32 nor ACOSOG Z0010 trials support routine use of multiple levels or IHC for detection of occult metastases 3
• No significant difference in 5-year overall survival or disease-free survival between patients with and without IHC-detected occult metastases 3
• Pathologists should quantify nodal tumor burden as part of standard analysis 3