How Many Lymph Nodes Are Sufficient for SLNB?
For breast cancer, removing at least 3 sentinel lymph nodes is recommended to achieve acceptable accuracy, as limiting the procedure to fewer nodes significantly increases the false-negative rate from 7.7% to 10.3%. 1
Disease-Specific Requirements
Breast Cancer
The optimal approach is to remove all sentinel lymph nodes until the procedure is complete, but at minimum 3 nodes should be excised when multiple nodes are present. 1, 2
- The false-negative rate increases significantly when limiting SLNB to fewer nodes (p<0.001), with removal of only 3 nodes associated with a 10.3% false-negative rate compared to 7.7% when more nodes are removed 1
- Approximately 98% of patients with lymph node metastases are identified by the 3rd sentinel node, while 100% are identified by the 4th node 2
- Removing a single sentinel node results in a false-negative rate of 14.3%, compared to 4.3% when multiple nodes are removed (p=0.0004) 3
- The first or second sentinel node independently determines axillary status in 99% of patients 4
The technical standard is to remove all nodes that meet any of these criteria: 1, 5
- Blue-stained nodes
- Nodes with radioactive counts ≥10% of the most radioactive node
- Nodes at the end of a blue lymphatic channel
- Palpably suspicious nodes
Melanoma
For melanoma, removal of the first 2 sentinel nodes is typically sufficient, as no patient had a positive third or subsequent node when the first two were negative. 5
- A mean of 1.9 sentinel nodes (median 2) per basin is removed 5
- The sentinel node with maximal radiotracer uptake and/or blue staining was pathologically positive in 95% of positive basins 5
- Removal of more than 2 sentinel nodes did not upstage any patient with primary melanoma 5
- Sentinel nodes should be evaluated with serial sectioning and immunohistochemistry 6
Oral/Oropharyngeal Squamous Cell Carcinoma
At least the 3 nodes with the highest radioactivity should be excised, with all positive sentinel nodes detected within the first 5 nodes of highest activity. 6
- Three-quarters of patients have 3 or fewer sentinel nodes 6
- For safety, all radioactive nodes should be excised 6
- Detection of more than 5 sentinel nodes is very rare 6
Technical Verification
After sentinel node excision, verify completeness by measuring residual radioactivity in the lymphatic basin. 6
- A count rate less than one-tenth that of the excised node with the lowest radioactivity indicates all sentinel nodes have been identified and removed 6
- Some centers use a threshold of one-tenth the "hottest" excised node, based on the Sunbelt Melanoma trial showing a 2% failure rate 6
Common Pitfalls and How to Avoid Them
Do not arbitrarily limit the procedure to a predetermined number of nodes—remove all nodes meeting technical criteria. 1, 5
- Stopping at 3 nodes when additional hot or blue nodes are present increases the false-negative rate 1
- The absolute radioactivity counts are less important than relative levels between excised nodes 6
Do not assume a specimen is adequate without pathologic confirmation of lymph node tissue. 7
- A specimen containing only fat represents a failed procedure requiring repeat mapping or formal axillary dissection 7
- Each sentinel node should be submitted in a separate cassette to permit accurate assessment 6, 7
For breast cancer after neoadjuvant chemotherapy, exercise particular caution with node count. 6