Sentinel node staging of primary melanoma by the “10% rule”: pathology and clinical outcomes

Background Surgical staging of clinically node-negative primary melanoma involves identification and removal of “sentinel” lymph nodes (SLNs). Although some suggest removal of only the “hottest” SLN, the “10% rule” dictates that nodes are removed until the background count is 10% or less of the count of the “hottest” node. Methods To determine the utility of the 10% rule, a university database of clinically node-negative melanomas surgically staged by using this rule was examined. Results Twenty-two of 177 cases (12.5%; 15% of T2 and T3 lesions) were SLN positive. Among the SLN-positive cases, use of the rule resulted in removal of 21 additional nodes, 7 of which contained tumor. In 3 cases (14%), the positive SLN was not the “hottest” node. At 49 months of mean follow-up time, overall survival was 63% for SLN-positive patients versus 92% for SLN-negative patients (P = .01). Conclusions Sentinel node staging of melanoma by the 10% rule provides significant prognostic information and a modest increase in tumor detection compared with removal of only the “hottest” node.