Sentinel lymph node biopsies in melanoma: how many nodes do we really need?

Sentinel lymph nodes (SLN) biopsy is a widely used method to detect lymphatic spread in patients with cutaneous melanoma. Several methods are used to detect SLNs. Recent reports attempted to identify the adequate number of SLNs to reliably detect malignant spread in regional lymph nodes.

The radiotracer counts and the pathologic reports of all patients undergoing SLN biopsies were collected prospectively, to determine which of the nodes harboring radiotracer needed to be removed for examination by histopathology between 1998 and 2005. All patients with positive SLN biopsies were investigated in the study. Lymph nodes were ranked according their radiotracer counts and numbered as hottest nodes, second hottest nodes, third hottest nodes, etc. The relationship between radioactivity and the risk of harboring malignancy was determined.

Nodal metastases were detected in 55 basins from 53 patients (10.5%). There was a correlation between the radiotracer uptake and risk of harboring malignancy. Excising the 3 hottest nodes and all blue nodes detected 100% of patients with lymphatic malignancy in our series. Most (98%) of positive lymph nodes had radiotracer counts greater than 30% of the hottest node. Only 1 patient (2%) had radioactive count less than 30%, but had visible blue dye.

Removing only the hottest node is inadequate to detect lymphatic spread. On the other hand, removing the 3 hottest nodes and all visible blue nodes is sufficient to detect regional lymphatic spread in patients with cutaneous melanoma. Removing nodes with a radiotracer uptake less than 30% of the hottest nodes may be unnecessary.