(LSM P3) Active Surveillance of Melanoma Patients with Sentinel Node Metastasis: An International Multi-Institution Evaluation of post-MSLT-2 Adoption and Early Outcomes

Introduction: For surgically resected cutaneous melanoma with positive sentinel lymph nodes (SLN), the Multicenter Selective Lymphadenectomy Trial 2 (MSLT2) demonstrated equivalent melanoma-specific survival with active surveillance (AS) using nodal basin ultrasound (US) versus immediate completion lymphadenectomy (CLND).

Methods: We retrospectively evaluated adoption of AS and early oncologic outcomes in SLN+ patients from 6/2017–6/2019. Using Cox proportional hazards models, we explored the impact of AS and adjuvant systemic therapy (ADJ) on overall recurrence (OR) and isolated nodal basin recurrence (INBR).

Results: Across 15 institutions 4194 SLNB were performed, of which 782 had +SLN and negative staging (19%). 167 patients underwent CLND (21%), 615 (79%) received AS. CLND was more common for younger patients, head/neck tumors, more +SLNs, extra-nodal extension (ENE), and larger nodal deposits (all p<0.05). For nodal surveillance, 11 institutions used US while 4 used CT. 294 patients (38%) received ADJ (84% anti-PD1). ADJ correlated with adverse tumor/nodal features (ulceration, more +SLNs, ENE, larger nodal deposits, and higher pathologic stage all p<0.001). At 10.3 months median follow-up 42 patients had INBR (post-CLND 6/167 (3.6%), AS 36/615 (5.9%)) and 107 (13.7%) recurred at local, distant, or multiple sites. In adjusted analyses CLND and ADJ were associated with decreased OR but not NBR.

Conclusions: With high adoption of AS, short-term INBR was uncommon. Higher risk patients more often received CLND and ADJ, which were associated with reduced OR. Nodal observation appears appropriate for most patients. Future work should address when CLND remains beneficial and which AS patients benefit from ADJ.