What if a Sentinel Lymph Node Biopsy (SLNB) is suboptimal and only contains fat?

Management of Suboptimal Sentinel Lymph Node Biopsy Containing Only Fat

When a sentinel lymph node biopsy specimen contains only fat without identifiable lymph node tissue, this represents a failed or inadequate procedure that requires repeat sentinel lymph node mapping and biopsy, or proceeding directly to formal axillary lymph node dissection if repeat mapping is not feasible. 1

Understanding the Problem

A specimen containing only fat indicates that no actual lymph node tissue was retrieved during the procedure. This is fundamentally different from a negative sentinel lymph node—it means the sentinel node was never actually sampled. 1

• Pathologists receive either single lymph nodes dissected free of fat or axillary fat containing one or more lymph nodes, and fatty nodules must be carefully dissected to identify all lymph nodes. 1 When only fat is present after this careful dissection, no lymph node was successfully removed.

• For the sentinel lymph node approach to be effective, surgeons must identify and remove all true sentinel lymph nodes, and pathologists must carefully and systematically examine them. 1 A specimen with only fat fails this fundamental requirement.

Immediate Management Algorithm

Step 1: Confirm the Pathology Finding

• Ensure the pathologist has thoroughly examined the specimen with careful dissection of all fatty tissue to confirm no lymph node tissue is present. 1
• Each sentinel lymph node should be submitted in a separate cassette or identified by colored ink to permit accurate assessment. 1

Step 2: Determine if Additional Sentinel Nodes Were Retrieved

• If multiple specimens were sent and at least one contains identifiable lymph node tissue, the procedure may still be considered adequate depending on the number of nodes retrieved. 2
• Removal of at least 3-4 sentinel lymph nodes is associated with improved accuracy, with false-negative rates dropping to 0% when four or more nodes are removed. 2

Step 3: Management Based on Clinical Context

If this is the only specimen retrieved (no lymph node tissue obtained):

• Repeat sentinel lymph node mapping and biopsy should be performed if technically feasible. 1 The original injection sites may still allow identification of additional sentinel nodes.

• If repeat mapping is not feasible or fails, proceed to formal level I and II axillary lymph node dissection to ensure adequate staging. 1, 3 This is particularly important for patients with:

  • Tumors >1.0 mm thickness (melanoma) 1
  • Stage IB or II melanoma 1
  • Breast cancer requiring accurate nodal staging for treatment decisions 1

If other sentinel nodes were successfully retrieved:

• The adequacy depends on the total number of lymph nodes obtained. 2 With 3-4 or more nodes successfully retrieved from other specimens, the procedure may be considered adequate despite one specimen containing only fat.

• The false-negative rate is 26.6% for a single sentinel node, 8.0% for two nodes, and drops to 0% when four or more nodes are removed. 2

Technical Considerations to Prevent This Problem

• Intraoperative confirmation using a gamma probe should verify radioactive counts in the excised tissue before concluding the procedure. 1 Tissue with counts significantly above background confirms lymph node tissue is present.

• Visual inspection for blue dye (if used) and palpation for firm nodular tissue within the fat can help identify lymph nodes intraoperatively. 1

• Lymphoscintigraphic imaging before surgery can demonstrate the expected location and number of sentinel nodes, guiding more complete removal. 1

Disease-Specific Considerations

For Melanoma:

• Meticulous pathologic examination of all sentinel nodes is mandatory, with serial sectioning and immunohistochemical staining. 1 A specimen with only fat provides no staging information.

• For patients with stage IB or II melanoma (≤1.0 mm thick with ulceration or mitotic rate ≥1 per mm² or >1.0 mm thick), sentinel lymph node biopsy should be discussed and offered. 1 Failure to obtain lymph node tissue necessitates repeat attempt or formal dissection.

For Breast Cancer:

• Accurate identification of node metastases is the firm basis on which appropriate treatment decisions are made. 1

• When formal axillary dissection is performed, at least 10 lymph nodes must be examined for accurate staging. 3 This standard applies if proceeding to completion dissection after failed sentinel node biopsy.

Common Pitfalls and How to Avoid Them

• Do not assume a specimen is adequate based solely on visual appearance or size—pathologic confirmation of lymph node tissue is essential. 1

• Do not proceed with observation alone when no lymph node tissue was obtained, as this leaves the patient unstaged and potentially undertreated. 1, 4

• Avoid accepting a single "hot spot" as adequate—multiple sentinel nodes often exist, and removing 3-4 nodes significantly improves accuracy. 2

• Do not delay addressing this issue—staging information is critical for determining adjuvant therapy, and delayed procedures may be more technically challenging. 1, 4