Sentinel lymph node biopsy for melanoma: is there a correlation of preoperative lymphatic mapping with sentinel lymph nodes harvested?

BACKGROUND: Nodal status is the most significant prognostic factor in melanoma. No study has examined the relationship between lymphoscintigraphy, γ probe counts, harvested nodes, and nodal status. METHODS: Two-hundred sixty two patients were identified who underwent sentinel lymph node biopsy for melanoma between 2001 and 2010. Clinicopathologic and treatment information was collected. The number of lymph nodes and basins demonstrated on lymphoscintigraphy was compared to those at surgery. γ Probe counts were compared. RESULTS: Median age was 54.5 years (range, 18-90 years) with 52.3% male. Average Breslow depth was 2.0 (1.9) mm; 99.6% of lymphoscintigraphy studies identified at least 1 basin, 80% showed only 1 (range, 0-4). Lymphoscintigraphy identified on average 1.5 (0.9) sentinel nodes and 31% with secondary node. Surgery excised on average 2.6 (1.4) nodes involving 1.2 (0.5) basins; 17.6% had a positive sentinel lymph node. There was no difference in the sum or average of γ counts between positive and negative sentinel lymph node groups (P = 0.2, P = 0.5). When comparing lymphoscintigraphy and surgical excision, the correlation of lymphatic basins was r = 0.67 and of lymph node numbers was r = 0.33. CONCLUSIONS: Lymphoscintigraphy should be used to identify the proper lymphatic basins for a sentinel node procedure, however, the removal of nodes must continue until the background count is less than 10%. The correlation of lymph node number identified on lymphoscintigraphy to surgical excision is weak. γ Probe counts cannot be used to differentiate positive from negative nodes and the positive lymph node is not always the hottest node.