Management Protocol for Sentinel Lymph Node Biopsy with Microinvasion
When microinvasion is detected on the first sentinel lymph node sampled, proceed with completion axillary lymph node dissection (ALND), as patients with micrometastatic disease in sentinel nodes have a significant risk of additional positive non-sentinel nodes. 1
Immediate Pathologic Confirmation
Verify the pathologic classification using AJCC/UICC staging criteria: micrometastases are defined as tumor deposits >0.2 mm but ≤2.0 mm and classified as pN1mi, while isolated tumor cells (ITC) ≤0.2 mm are classified as pN0(i). 2
Document the maximal size of the largest tumor cluster and the pattern of metastasis (single cells, clusters, or confluent deposits) in the pathology report. 2
Ensure accurate node counting: coordinate between the surgeon and pathologist to avoid over-recording bisected or serially sectioned positive sentinel nodes as multiple positive nodes. 2
Surgical Management Algorithm
For True Micrometastases (>0.2 mm to 2.0 mm):
Perform completion ALND during the same operative session if micrometastases are detected on intraoperative assessment, or schedule a second procedure if detected on permanent sections. 1
The rationale: In the multi-institutional series of ductal carcinoma in situ with microinvasion (DCISM), all four patients with positive sentinel nodes who underwent completion ALND had additional metastatic axillary nodes identified. 1
Remove level I and II axillary lymph nodes during completion dissection, preserving the long thoracic nerve (C5-C7) and thoracodorsal nerve to prevent serratus anterior and latissimus dorsi dysfunction. 3
For Isolated Tumor Cells (≤0.2 mm):
Consider observation without completion ALND for ITC, as these are classified as pN0(i) and have minimal clinical significance. 2
The evidence: In microinvasive carcinoma series, only 3% had isolated tumor cells in sentinel nodes, with no cases showing micrometastases or macrometastases in additional nodes, and no axillary recurrences at median 37-month follow-up. 4
Pathologic Processing Requirements
Cut sentinel nodes into perimeridianal slices ≤2 mm thick and examine full cross-sections with H&E staining at minimum. 2
Perform step sections at 200-500 μm intervals rather than superficial serial sections alone, as this detects additional micrometastases more effectively. 2
Submit each sentinel node in a separate cassette or mark with colored ink to permit accurate assessment of total node count and number of involved nodes. 2
Consider immunohistochemistry with cytokeratin antibodies to facilitate detection of small tumor deposits, though routine IHC is not currently mandated by ASCO guidelines. 2
Critical Pitfalls to Avoid
Do not assume a negative result if only fat was submitted: This represents a failed procedure requiring repeat sentinel node mapping or formal ALND if repeat mapping is not feasible. 5
Do not rely solely on intraoperative assessment: Approximately 8-9 false-negative results occur per 100 patients evaluated intraoperatively, with only 16-17 true positives detected. 2, 3
Do not under-stage based on single-node sampling: False-negative rates are 31% when only one sentinel node is removed versus 12% when two nodes are removed in breast cancer patients. 6
Verify radioactive counts intraoperatively: Residual radioactivity in the lymphatic basin should be less than one-tenth that of the excised node with lowest radioactivity to confirm complete sentinel node removal. 6
Special Considerations for DCIS with Microinvasion
The upstaging rate is substantial: 42.6% of DCIS patients undergoing mastectomy are upgraded to invasive carcinoma, with 13.8% showing microinvasion. 7
Sentinel node positivity in DCISM is 9.3%, justifying routine sentinel node biopsy given the low morbidity of the procedure. 1
High nuclear grade DCIS and HER2-amplified DCIS are associated with greater risk of microinvasion and invasion, warranting heightened vigilance. 8
For mastectomy patients with DCIS, perform upfront sentinel node biopsy as subsequent node mapping is not feasible, and this avoids unnecessary ALND for two-thirds of patients with micro or invasive disease. 9, 8