Implications of wait times for sentinel node biopsy on melanoma disease progression, micrometastatic tumour burden and survival outcomes in the modern treatment era

BACKGROUND: Sentinel node biopsy (SNB) predicts long-term melanoma outcomes and advises referrals for adjuvant systemic therapy (AST). Concerns regarding the impact of treatment delays on clinical outcomes remain. METHODS: A UK retrospective cohort study at a supra-regional centre was performed, including 1625 patients listed for SNB between 2010-23. Three parameters were investigated: disease progression, micrometastatic burden, and disease-specific survival. Time-to-SNB was stratified as early (≤90days) or late (>90days), with a subgroup analysis accounting for AST use (2017-23). Sensitivity analyses calculated a wait-time threshold beyond which worsens survival outcomes. RESULTS: Median time-to-SNB was 68 days (IQR = 51-95) and follow-up 75 months (IQR = 35-115). Late surgery correlated with disease progression before surgery (0.34% versus 1.54%; OR = 4.31; p = 0.022); larger micrometastases (1.40 mm vs. 2.95 mm; p = 0.003), and increased high-risk micrometastatic deposits >1 mm (55.2% vs. 69.1%; OR = 2.04; p = 0.014). For patients post-2016, longer wait-times correlated with poorer DSS (HR = 1.01 (1.00-1.02); p = 0.011 for diagnosis-to-SNB; and HR = 1.01 (1.00-1.02); p = 0.016 for primary excision-to-SNB). Sensitivity analyses calculated ≤68-days from diagnosis (HR = 3.17 (1.19-8.46); p = 0.021) and ≤82-days from excision (HR = 2.94 (1.10-7.87); p = 0.032) as optimal treatment thresholds. CONCLUSION: Surgical delays correlated with harm: disease progression, increased tumour burden and worse survival. SNB should occur within 68 days from diagnosis and/or 82 days from excision biopsy.