What are the indications for Sentinel Lymph Node Biopsy (SLNB) in breast cancer patients?

Indications for Sentinel Lymph Node Biopsy in Breast Cancer

Standard Indications

SLNB is the standard of care for clinically node-negative early-stage breast cancer (T1-T2, stages I-II) undergoing upfront surgery, replacing routine axillary lymph node dissection for axillary staging. 1

Primary Candidates for SLNB

• Small invasive tumors (T1-T2, ≤5 cm) with clinically negative axillary nodes are the primary indication for SLNB 1, 2
• Clinically node-negative patients confirmed by physical examination and negative preoperative axillary ultrasound 1
• Patients undergoing either breast-conserving surgery or mastectomy are appropriate candidates 1, 3

Special Circumstances Where SLNB May Be Offered

The 2025 ASCO guideline expanded indications to include several special populations 1:

Tumor Characteristics

• Multicentric tumors (clinically node-negative) - SLNB can be performed using subareolar or intradermal injection techniques that identify sentinel nodes for the entire breast 1
• cT3-T4c tumors (clinically node-negative) - SLNB may be offered despite larger tumor size 1

DCIS-Specific Indications

• DCIS treated with mastectomy - SLNB should be considered to avoid a second operation if invasive cancer is found on final pathology (10-20% upstaging rate) 1
• Large or high-grade DCIS undergoing mastectomy or immediate reconstruction, as axillary staging becomes impossible after reconstruction 1

Patient-Specific Factors

• Obese patients - SLNB remains feasible despite slightly lower success rates with increasing body mass index 1
• Male breast cancer - SLNB is appropriate for staging 1
• Pregnant patients - SLNB may be offered (using radiotracer without blue dye to avoid fetal exposure) 1
• Prior breast or axillary surgery - SLNB can be performed with acceptable accuracy using alternative injection techniques 1

After Neoadjuvant Therapy

• Patients with clinically positive nodes that become clinically negative after neoadjuvant chemotherapy may be candidates for SLNB rather than mandatory ALND 1, 3

When SLNB Can Be Omitted

SLNB should not be routinely recommended in highly select postmenopausal patients ≥50 years with grade 1-2, hormone receptor-positive, HER2-negative tumors ≤2 cm with negative preoperative axillary ultrasound undergoing breast-conserving therapy. 1, 4

This represents a significant paradigm shift allowing omission of axillary surgery entirely in this low-risk population 1.

Contraindications and Situations Where SLNB Should NOT Be Performed

Absolute Contraindications

• Inflammatory breast cancer - false-negative rates are unacceptably high due to obstructed subdermal lymphatics containing tumor emboli 1
• Clinically suspicious or palpable axillary lymph nodes - these patients require direct sampling or ALND rather than SLNB 1, 4
• N2/N3 stage disease (fixed or matted nodes, infraclavicular or supraclavicular involvement) 4

Relative Contraindications (Insufficient Evidence)

• DCIS treated with breast-conserving surgery - SLNB is not routinely recommended as the risk of nodal metastases is <1% 1
• Large locally advanced tumors (T3/T4) without neoadjuvant therapy - insufficient data, though this is evolving with the 2025 guideline allowing SLNB for cT3-T4c if clinically node-negative 1

Technical Requirements for Appropriate SLNB Use

SLNB should only be performed by surgeons with demonstrated low false-negative rates (<10%) and high successful mapping rates (>90%). 1, 4

Key Technical Factors

• Dual technique using both radiotracer and blue dye achieves the highest success rates and lowest false-negative rates compared to single-agent techniques 1, 5
• Multiple sentinel nodes should be removed when identified (average 1-3 nodes) 6
• Complete clinical examination of the axilla must be performed intraoperatively to avoid missing palpable metastases that may cause false-negative SLNB 2

Critical Pitfalls to Avoid

• Do not rely solely on imaging (ultrasound, MRI, PET) to determine nodal status - these have unacceptable false-negative rates for small metastases 1, 4
• Do not default to ALND for micrometastases detected only by immunohistochemistry - these patients do not require completion ALND 4
• Failed or technically unsatisfactory SLNB procedure requires default to ALND 1, 4

Clinical Decision Algorithm

For clinically node-negative early-stage breast cancer:

1. Low-risk patients (postmenopausal, ≥50 years, grade 1-2, HR+/HER2-, ≤2 cm, negative axillary ultrasound, breast-conserving therapy) → Consider omitting SLNB entirely 1, 4

2. Standard early-stage patients (T1-T2, clinically node-negative) → Perform SLNB 1

3. Special circumstances (multicentric, cT3-T4c, DCIS with mastectomy, obese, male, pregnant, prior surgery) → May offer SLNB 1

4. Contraindicated patients (inflammatory breast cancer, clinically positive nodes, N2/N3 disease) → Proceed directly to ALND 1, 4

5. After neoadjuvant therapy → SLNB may be performed if nodes become clinically negative 1, 3