What is a sentinel node? Re-evaluating the 10% rule for sentinel lymph node biopsy in melanoma.
BACKGROUND
Many surgeons use the "10% rule" to define whether a lymph node is a sentinel node (SLN) when staging malignant melanoma. However, this increases the number of SLN removed and the time and cost of the procedure. We examined the impact of raising this threshold on the accuracy of the procedure.


METHODS
We reviewed the records of 561 patients with melanoma (624 basins) who underwent SLN with technetium Tc99 labeled sulfur colloid using a definition of a SLN as 10% of that of the node with the highest counts per minute (CPM).


RESULTS
Of the 624 basins, 154 (25%) were positive for metastases. An average of 1.9 nodes per basin were removed (range 1-6). Metastases were found in the hottest node in 137 cases (89% of positive basins, 97% of basins overall). Increasing the threshold above 10% decreased the number of nodes excised and the costs involved, but incrementally raised the number of false negative cases above baseline (a 4% increase for a "20% rule," 5% for a "30% rule," 6% for a "40% rule," and 7% for a "50% rule"). Taking only the hottest node would raise the false negative rate by 11%.


CONCLUSIONS
Although using thresholds higher than 10% for the definition of a SLN will minimize the extent of surgery and decrease the costs associated with the procedure, it will compromise the accuracy of the procedure and is not recommended.
Kroon
Hidde M
HM
Department of Surgery, University of Michigan Comprehensive Cancer Center, Ann Arbor, Michigan 48105, USA.
Lowe
Lori
L
Wong
Sandra
S
Fullen
Doug
D
Su
Lyndon
L
Cimmino
Vincent
V
Chang
Alfred E
AE
Johnson
Timothy
T
Sabel
Michael S
MS
D003362:Cost-Benefit Analysis; D005188:False Negative Reactions; D005260:Female; D006801:Humans; D008197:Lymph Node Excision; D008198:Lymph Nodes / Q000473:pathology*; D008207:Lymphatic Metastasis; D008297:Male; D008545:Melanoma / Q000473:pathology* / Q000556:secondary / Q000601:surgery; D021701:Sentinel Lymph Node Biopsy / Q000191:economics / Q000379:methods; D012878:Skin Neoplasms / Q000473:pathology* / Q000601:surgery; D013671:Technetium Tc 99m Sulfur Colloid
D013671:Technetium Tc 99m Sulfur Colloid