When is Sentinel Lymph Node Biopsy (SLNB) indicated?

When is Sentinel Lymph Node Biopsy (SLNB) Indicated?

SLNB is indicated for clinically node-negative early-stage breast cancer (T1-T2, stages I-II) undergoing upfront surgery, and for melanoma patients with stage IB or II disease (>1.0 mm thick or ≤1.0 mm with ulceration/Clark level IV-V). 1, 2

Breast Cancer Indications

Standard Indications

• Clinically node-negative patients with T1-T2 invasive breast cancer (≤5 cm) confirmed by physical examination and negative preoperative axillary ultrasound should undergo SLNB. 1, 2
• Both breast-conserving surgery and mastectomy patients are appropriate candidates. 2
• SLNB has replaced routine axillary lymph node dissection as the standard of care for axillary staging in early-stage disease. 1, 2

When SLNB Can Be Omitted in Breast Cancer

Routine SLNB should NOT be performed in highly selected patients who are postmenopausal, ≥50 years old, with grade 1-2, small (≤2 cm), hormone receptor-positive, HER2-negative breast cancer, negative preoperative axillary ultrasound, and undergoing breast-conserving therapy. 1, 2

• This omission requires multidisciplinary discussion of adjuvant therapy options prior to surgery. 1
• If suspicious nodes are visualized on ultrasound, fine-needle aspiration (FNA) must be performed and confirmed benign before omitting SLNB. 1
• Breast MRI may help confirm tumor size ≤2 cm when considering SLNB omission. 1

Special Circumstances in Breast Cancer Where SLNB May Be Offered

• Multicentric tumors (clinically node-negative) - using subareolar or intradermal injection techniques. 1, 2
• cT3-T4c tumors (clinically node-negative) - despite larger tumor size. 1, 2
• DCIS treated with mastectomy - to avoid second operation if invasive cancer found on final pathology (10-20% upstaging rate). 1, 2
• Large or high-grade DCIS undergoing mastectomy or immediate reconstruction - axillary staging becomes impossible after reconstruction. 2
• Obese patients - SLNB remains feasible despite slightly lower success rates. 1, 2
• Male breast cancer - appropriate for staging. 1, 2
• Pregnant patients - using radiotracer without blue dye to avoid fetal exposure. 1, 2
• Prior breast or axillary surgery - using alternative injection techniques. 1, 2

After Neoadjuvant Chemotherapy in Breast Cancer

• Initially clinically node-negative patients should undergo SLNB after neoadjuvant chemotherapy with false-negative rates of 5.9-12%. 3
• Initially node-positive patients who convert to clinically node-negative after neoadjuvant therapy may undergo SLNB if: 3
  • Dual tracer method is used (radiotracer and blue dye)
  • At least 3 sentinel nodes are removed
  • Previously biopsied/clipped node is removed (targeted axillary dissection)
  • Initial disease was limited (pN1, not cN2-3)
• Clip placement in biopsied nodes before neoadjuvant therapy is essential, reducing false-negative rates to 0-7%. 3

Breast Cancer Contraindications to SLNB

• Inflammatory breast cancer (T4d) - false-negative rates are unacceptably high due to obstructed subdermal lymphatics. 2, 3
• Clinically suspicious or palpable axillary lymph nodes - require direct sampling or axillary lymph node dissection. 2
• N2/N3 stage disease (fixed/matted nodes, infraclavicular or supraclavicular involvement). 2
• Initial bulky nodal involvement (cN2-3) even after neoadjuvant therapy. 3

Melanoma Indications

Standard Indications

• SLNB is NOT recommended for in situ melanoma (stage 0) or stage IA melanoma ≤1.0 mm without adverse features. 1
• SLNB should be discussed for stage IA thin melanomas (≤1.0 mm) with adverse features: 1
  • Thickness >0.75 mm
  • High mitotic rate
  • Young patient age
  • Positive deep margins (individual basis)
  • Lymphovascular invasion (individual basis)
• SLNB is encouraged for stage IB or II melanoma: 1
  • ≤1.0 mm thick with ulceration or Clark level IV-V

  • 1.0 mm thick

• Thick melanomas (≥4 mm) have 30-40% probability of positive sentinel node; SLNB helps define prognostically homogeneous groups for adjuvant therapy trials. 1

Melanoma Technical Requirements

• Sentinel nodes must be evaluated with serial sectioning and immunohistochemistry. 1
• Wide excision before planned SLNB is discouraged as it compromises mapping accuracy. 1
• Patients may be considered for SLNB on individual basis if presenting after initial wide excision. 1

Technical Requirements Across All Indications

• SLNB should only be performed by surgeons with demonstrated false-negative rates <10% and successful mapping rates >90%. 2
• Dual technique using both radiotracer and blue dye achieves highest success rates and lowest false-negative rates. 2, 3
• Complete clinical examination of the axilla must be performed intraoperatively to avoid missing palpable metastases. 2
• Intraoperative gamma probe confirmation should verify radioactive counts in excised tissue. 4

Common Pitfalls and How to Avoid Them

• Do not perform SLNB before neoadjuvant therapy even in clinically node-negative patients, as this compromises ability to assess treatment response. 3
• Do not rely on clinical examination alone - ultrasound identifies occult nodal disease in clinically node-negative patients. 3
• If only fat is obtained without lymph node tissue, this represents a failed procedure requiring repeat mapping or formal axillary dissection. 4
• Do not assume adequacy based on visual appearance - pathologic confirmation of lymph node tissue is essential. 4
• For melanoma, do not perform routine elective lymph node dissection if SLNB is unavailable; wide excision alone or referral to a center with lymphatic mapping are acceptable. 1