17 | The role of sentinel lymph node biopsy in pt1a, pt1b and pt2a melanomas: a 10-year experience through 2025

Gabriele Roccuzzo¹, Nicolas Destefanis², Giulia Orlando³, Eleonora Bergamo¹, Virginia Caliendo⁴, Adriana Lesca⁵, Daniela Zugna², Franco Picciotto⁴, Rebecca Senetta³, Simone Ribero¹, Pietro Quaglino¹ | ¹Department of Medical Sciences, Section of Dermatology, University of Turin; ²Cancer Epidemiology Unit, Department of Medical Sciences, University of Turin; ³Department of Oncology, Section of Surgical Pathology, University of Turin; ⁴Dermatologic Surgery Section, Department of Surgery, Azienda Ospedaliera Universitaria Città della Salute e della Scienza, Turin; ⁵Division of Nuclear Medicine, Department of Medical Science, University of Turin, Italy.

Background: Sentinel lymph node biopsy (SLNB) is key for melanoma staging, but its value in thinner lesions is debated, with current predictive models often underestimating positivity.

Methods: We retrospectively analyzed 511 patients with pT1a (8.6%), pT1b (36.4%), and pT2a (54.9%) melanomas, who underwent SLNB at the University of Turin (2014–2020, follow up to 1.2025) and did not receive subsequent adjuvant therapy. Multivariable logistic and Cox regression models were applied, addressing missing data via multiple imputation. SLN deposit size cut-offs were tested for prognostic value. Calibration models assessed prediction accuracy for SLNB status, disease-free survival (DFS), and overall survival (OS).

Results: SLN positivity occurred in 12.9% of patients, more often in pT2a (p=0.022). Breslow thickness was the only independent predictor (OR 3.17, 95%CI 1.52–6.63). 5- and 10-year DFS were 90.9% and 86.0%, and OS 94.8% and 85.3%. DFS was worse for pT2a (79.9% at 10 years) versus pT1a (97.5%) and pT1b (92.6%) (p<0.001). SLNB positivity predicted shorter DFS (HR 2.31, 95%CI 1.25–4.27), alongside Breslow thickness, mitotic rate, and ulceration. In contrast, the number of positive SLNs—but not SLNB status—predicted OS (HR 1.84 per additional positive SLN, 95%CI 1.13–3.01), along with age and mitotic rate. CLND revealed additional nodal metastases in only 7.7% and did not improve survival. Patients with SLN deposits ≤0.3 mm had no recurrences over 10 years (p=0.0285), depicting a better prognostic stratification than 0.4 mm cut-off.

Discussion: In pT1a–pT2a melanoma, SLN positivity is uncommon and primarily linked to Breslow thickness. Prognostic roles differ: SLNB status predicts recurrence, while the number of metastatic SLNs predicts death. SLN deposit ≤0.3 mm identifies a low-risk group who can safely avoid adjuvant therapy. Current clinicopathologic models underperform in very thin melanomas, underscoring the need for novel biomarkers to refine SLNB and treatment strategies.