Sentinel node studies in truncal melanoma: Does an increased number of draining basins correlate with an increased risk of lymph metastasis

Objectives To assess whether an association exists between drainage to multiple basins and lymphatic metastasis in patients with truncal melanoma.

Methods We retrospectively reviewed 128 patients with malignant melanoma between January 2006 and September 2008. All patients had an intradermal injection of ^99mTc-nanocolloid and lymphoscintigraphy followed by sentinel node biopsy. Pre-staging histology with Breslow thickness from excision biopsy was also obtained.

Results 46 (35.9%) patients were identified to have a truncal primary. Sentinel node histology was positive for metastatic disease in 17/46 (37.0%) patients. Of these 17, 7 had 1 drainage basin , 5 had 2 basins and 5 had 3 basins. Of the 29 negative, 22 had 1 basin, 6 had 2 basins and 1 had 3 drainage basins. Using Fisher exact test, we found a correlation with sentinel node positivity and those that had ≥2 basin drainage (p=0.02).

Results Breslow thickness was available in 32/46 (69.6%) patients, with 13/32 (40.6%) having a positive sentinel node biopsy. Of these, 1/2 patients had <1mm thickness, 5/16 had 1-2mm thickness, 3/7 had 2-4mm thickness and 4/7 had ≥4mm thickness. No correlation was found between Breslow thickness (comparing ≥4mm to <4mm) and nodal positivity (p-value 0.21).

Conclusions This study demonstrates that in patients with melanoma of the trunk, drainage to multiple basins significantly increases the probability of sentinel node metastasis. This may be related to formation of collaterals due to tumour blocking existing lymph channels, or may be a paracrine tumour effect, resulting in proliferation of lymphatic channels.