What is a Sentinel Lymph Node Biopsy (SLNB) in breast surgery?

What is a Sentinel Lymph Node Biopsy (SLNB) in Breast Surgery?

A sentinel lymph node biopsy (SLNB) is a minimally invasive surgical procedure that identifies and removes the first lymph node(s) to which breast cancer is most likely to spread, allowing accurate staging of the axilla while avoiding the significant morbidity of complete axillary lymph node dissection (ALND). 1

Core Concept and Rationale

SLNB is based on the principle that breast cancer spreads in an orderly fashion to one or a few lymph nodes—the sentinel lymph node(s)—before spreading to other axillary nodes. 1 These sentinel nodes can be reliably identified using vital blue dye, a radiolabeled colloid (technetium), or both techniques combined. 1

The procedure has replaced routine ALND as the standard of care for axillary staging in clinically node-negative early-stage breast cancer (T1-T2, stages I-II). 2 This shift occurred because ALND causes substantial morbidity including:

• Lymphedema (chronic arm swelling)
• Nerve injury
• Shoulder dysfunction
• Other complications that compromise quality of life 1

Technical Procedure

The surgical technique involves: 1

• Injection phase: A radiotracer and/or blue dye is injected into the breast tissue (periareolar, subareolar, or at the tumor site)
• Identification phase: The surgeon uses a handheld gamma probe to detect radioactivity and/or visually identifies blue-stained lymph nodes during surgery
• Removal phase: The sentinel node(s) are surgically excised through a small axillary incision
• Pathologic examination: The removed nodes undergo detailed histopathologic analysis, including serial sections and sometimes immunohistochemical staining 1

The dual technique using both radiotracer and blue dye achieves the highest success rates (>95% identification) and lowest false-negative rates (<10%) compared to single-agent techniques. 2

Clinical Significance and Accuracy

SLNB reliably predicts axillary node status in approximately 98% of all patients and 95% of node-positive patients. 3 When the sentinel node is negative for cancer, this accurately indicates that the remaining axillary nodes are also negative in the vast majority of cases. 1

Long-term data demonstrates that SLNB alone (without completion ALND) provides equivalent survival outcomes compared to ALND:

• 15-year follow-up shows no statistically significant differences in event-free survival (72.8% vs 72.9%) or overall survival (82.0% vs 78.8%) 4
• SLNB alone results in an 11.5% reduction in postsurgical complications compared to routine ALND 5

Standard Indications

SLNB is indicated for: 2

• Clinically node-negative patients (confirmed by physical examination and negative preoperative axillary ultrasound)
• Small invasive tumors (T1-T2, ≤5 cm)
• Early-stage breast cancer (stages I-II)
• Patients undergoing either breast-conserving surgery or mastectomy

Pathologic Reporting

The pathologist must carefully examine sentinel nodes and report findings using standardized AJCC/UICC criteria: 1

• Macrometastases: Tumor deposits >2.0 mm (classified as pN1)
• Micrometastases: Tumor deposits 0.2-2.0 mm (classified as pN1mi)
• Isolated tumor cell clusters (ITCs): Deposits ≤0.2 mm (classified as pN0[i])

Each sentinel node should be sectioned no thicker than 2 mm, with full-face cross-sections examined with hematoxylin and eosin staining. 1 The size of the largest tumor deposit must be documented, as this determines subsequent treatment decisions. 1

Clinical Decision-Making Based on Results

If sentinel nodes are negative: Completion ALND is not performed, as there is no survival advantage and significantly increased morbidity. 5, 4

If 1-2 sentinel nodes are positive: For patients receiving breast-conserving surgery with whole-breast radiotherapy, completion ALND can be safely omitted based on ACOSOG Z0011 trial criteria. 5 For mastectomy patients, post-mastectomy radiation with regional nodal irradiation may replace ALND. 5

If ≥3 sentinel nodes are positive: ALND followed by regional nodal irradiation is recommended. 5

Critical Technical Requirements

SLNB should only be performed by surgeons who have demonstrated: 2

• Low false-negative rates (<10%)
• High successful mapping rates (>90%)
• Completion of a formal learning curve with backup ALND validation 1

A carefully trained multidisciplinary team (surgeon, pathologist, nuclear medicine technician) is essential for reliable results. 1

Common Pitfalls to Avoid

Do not perform SLNB in: 2

• Inflammatory breast cancer (false-negative rates are unacceptably high due to tumor emboli obstructing lymphatics)
• Patients with clinically suspicious or palpable axillary nodes
• N2/N3 stage disease (fixed/matted nodes, supraclavicular involvement)

Technical errors to avoid: 2

• Failing to perform complete clinical examination of the axilla intraoperatively (may miss palpable metastases causing false-negative results)
• Using single-agent technique instead of dual tracer/dye approach
• Inadequate pathologic sectioning of sentinel nodes

Special Circumstances Where SLNB May Be Offered

The procedure can be performed with acceptable accuracy in: 2

• Multicentric tumors (using subareolar injection techniques)
• DCIS treated with mastectomy (to avoid second operation if invasive cancer found on final pathology)
• Prior breast or axillary surgery (using alternative injection techniques)
• Pregnant patients (using radiotracer without blue dye)
• Male breast cancer
• Obese patients (despite slightly lower success rates)

For DCIS treated with breast-conserving surgery, SLNB is not routinely recommended unless there is a mass lesion highly suggestive of invasive cancer or the DCIS area is large (≥5 cm). 1