The 10% Rule in Sentinel Node Biopsy: Is Removal of All Threshold Nodes Necessary?

Sentinel lymph node biopsy (SLNB) procedures have been guided by the "10% rule," which stipulates that any lymph node (LN) with gamma probe activity (GPA) measured at 10% of the most radioactive sentinel lymph nodes (SLNs) should be excised. We hypothesized that it would be unusual for a SLN with less than 20% GPA to harbor the only nodal metastasis in a patient.

Retrospective analysis.

Patients with head and neck cutaneous and oral malignancy who underwent SLNB at a tertiary medical center from 2013 to 2023.

All patients during this period had each SLN recorded with anatomic location and numerical GPA. SLNs which harbored metastatic disease were categorized by GPA, and, in particular, cases that met the 10% threshold, but were less than 20% of the hottest node, were highlighted.

A total of 93 patients presenting with head and neck malignancy that underwent SLNB were included in the study. In total, 433 SLNs were evaluated. Only 1 of these 93 patients (1.1% [95% CI: 1.0%-1.2%]) had a solitary positive SLN that was 10% to 20% of the hottest node and represented the only known SLN metastasis in that patient. In total, 36 patients (39% of patients) would have had one or more fewer SLN excisions without a change in their staging.

If seeking adherence to a 10% threshold complicates the procedure excessively or generates an excessive number of SLN excisions, a 20% threshold could be used. Based on our study, the risk of subsequent failure to diagnose nodal metastases would be acceptably low.