Exploring Geiger Count Thresholds for Sentinel Node Identification in Melanoma: Is 10 % Still Optimal?

Sentinel lymph node biopsies (SLNBs) carry risk. Therefore, refinement of sentinel lymph node (SLN) identification protocols may improve patient safety. Currently, the 10 % Geiger count threshold is standard for SLN identification, yet the utility of more restrictive thresholds remains unexplored. This study explored whether a 30 % threshold could maintain diagnostic reliability while reducing the number of nodes removed.

A single-institution, retrospective review of all malignant melanoma patients who underwent SLNB with technetium-99m sulfur colloid (99mTc) lymphatic mapping with or without methylene blue dye was performed. Only patients with at least two SLNs, preoperative clinical staging, and reported final pathology were considered for analysis. Individual SLN Geiger counts were calculated as fractions of the highest count value (percent hottest node [PHN]) found in the associated LN basin. Positive and negative predictive values were calculated and compared for the cohort using the gold standard 10 % and experimental 30 % Geiger count thresholds. Pathologic stage was determined for patients who had pathologically positive SLNs that remained unidentified by the 30 % count threshold.

The study included 1,001 patients with 1,098 involved LN basins. Compared with the traditional 10 % threshold, the 30% threshold was associated with a higher positive predictive value and a comparable negative predictive value across all LN basins sampled and upon stratification by tumor preoperative T stage. The optimal Geiger count threshold was calculated to be 52.3 % for this cohort.

In this exploratory retrospective review, a 30 % Geiger count threshold appeared to identify SLNs without compromising disease detection. These results suggest that higher thresholds may suffice for accurate staging and merit prospective evaluation.