Sentinel lymph node biopsy for cutaneous melanoma performed within 6 weeks of diagnostic excision compared to those performed at longer time intervals in a UK cohort

Objectives: The impact of optimal timing of sentinel lymph node biopsy (SLNB) in cutaneous melanoma remains debated, with guidelines recommending a three-month window post-diagnosis.Our study investigates the time interval to perform SLNB in relation to SLN positivity and long-term outcomes.Methods: This single-centre retrospective observational cohort included all adult patients with a melanoma undergoing SLNB between 2009 and 2022 at a UK University hospital.Patients were categorised into those who had SLNB performed in 42 days, or > 42 days.Kaplan-Meier survival analysis compared recurrence-free survival (RFS) and melanoma-specific survival (MSS).The size of the largest metastatic foci was recorded, and multiple logistic regression identified independent predictors.Results: 1393 patients were included with a median follow-up of 4.5 years (IQR 1.9-7.3yrs) and median time to SLNB of 66 days.The SLNB positivity, RFS and MSS were no different between the SLNB 42days or > 42 days (229 % vs 209 %, p = 0.531; Log-rank p = 0.655 and 0.225).The median size of lymph node micro-metastasis increased from 0.7 mm (IQR 0.275-1.8mm) for patients with positive SLNB 6 weeks, 0.8 mm (IQR 0.3-2.0mm) for patients between 6 and 12 weeks, and 1.5 mm (IQR 0.5-5.0mm) > 12 weeks [one-way ANOVA trend= 0.0065].A micro-metastasis doubling time of 6.8 weeks, and average time lag from seeding of 11months were inferred.Conclusions: Time interval to perform SLNB does not significantly affect lymph node seeding but allows modest increase in size of any lymph node micro-metastasis.This is not translated to a clinical benefit for SLNB performed within 6 weeks of diagnosis in MSS or RFS.