Prognostic Significance of Sentinel Lymph Node Status in Thick Primary Melanomas (> 4 mm)

The key prognostic factors for staging patients with primary cutaneous melanoma are Breslow thickness, ulceration, and sentinel lymph node (SLN) status. The multicenter selective lymphadenectomy trial (MSLT-I) verified SLN status as the most important prognostic factor for patients with intermediate-thickness melanoma (Breslow thickness, 1-4 mm). Although most international guidelines recommend SLN biopsy (SLNB) also for patients with thick (> 4 mm, pT4) melanomas, its prognostic role has been questioned. The primary aim of this study was to establish whether SLN status is prognostic in T4 melanoma tumors.

Data for all patients with a diagnosis of primary invasive cutaneous melanoma of Breslow thickness greater than 1 mm in Sweden between 2007 and 2020 were retrieved from the Swedish Melanoma Registry, a large prospective population-based registry. A multivariable Cox proportional hazard model for melanoma-specific survival (MSS) was constructed based on Breslow thickness stratified for SLN status.

The study enrolled 10,491 patients, 1943 of whom had a Breslow thickness greater than 4 mm (pT4). A positive SLN was found for 34% of these pT4 patients. The 5-year MSS was 71%, and the 10-year MSS was 62%. There was a statistically significant difference in MSS between the patients with a positive SLN and those with a negative SLN (hazard ratio of 2.4 (95% confidence interval CI 1.6-3.5) for stage T4a and 2.0 (95% CI 1.6-2.5) for satage T4b.

Sentinel lymph node status gives important prognostic information also for patients with thick (> 4 mm) melanomas, and the authors thus recommend that clinical guidelines be updated to reflect this.