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Enhanced risk of multiple sentinel lymph node basins in truncal and head and neck melanoma

Introduction: Truncal and head and neck melanomas have a greater propensity to drain to multiple lymph node basins (MLNB) compared to extremity melanomas, which drain predominantly to a single lymph node basin (SLNB). The objective of this study was to compare the lymphatic drainage patterns and characteristics of truncal and head and neck melanoma, to assess their clinical usefulness in areas of unpredictable drainage. 
Methods: A retrospective review of 143 patients with head and neck or truncal melanoma from 2014–2018 treated at a tertiary referral hospital in Melbourne, Australia. Patients scheduled for a wide local excision (WLE) and SeNBx, and those whose initial biopsy results stated melanoma type, cell type and BT, were included. Patients were excluded if they underwent nodal biopsy alone.
Results: We identified 95 patients with truncal and 48 with head and neck melanoma. Drainage to MLNB was significantly higher in the truncal melanoma group (36.8%) compared to the head and neck group (10.4%) (P = 0.001). Patients with drainage to MLNB had a higher positive sentinel node biopsy (SeNBx) rate compared to those with SLNB (40.0% verus. 12.6%, P <0.0001). Truncal melanomas that drained to MLNB were associated with a significantly higher Breslow thickness (2.1 versus. 1.5, P = 0.02), ulceration (40.6% vs. 20.7%, P = 0.043) and mitotic rate (3.0 versus. 2.0, P = 0.045) compared to equivalent melanomas that drained to SLNB. 
Conclusion: Patients with melanomas occurring in the trunk exhibit higher rates of drainage to MLNB compared to melanomas arising in the head and neck. Patients with drainage to MLNB also demonstrate a higher rate of positive SeNBx than those with SLNB drainage. This may represent more aggressive disease pathology or later diagnosis of lesions within these locations, or a lymphatic system that is more facilitatory of spread.