Disease progression in melanoma patients with negative sentinel lymph node: does false-negative specimens entirely account for this phenomenon?

Background Sentinel lymph node (SLN) status is the most important prognostic factor for subjects with primary melanoma thicker than 1 mm. Objective We focused our study on patients with disease progression after negative SLN biopsy (SLNB), with the aim of elucidating their clinical and histopathological characteristics, outcome and real incidence of false negative. Methods A total of 688 melanoma patients who underwent SLNB (1 May 1998-31 December 2008) were analysed; all patients had Breslow > 1 mm or Breslow < 1 mm and at least one of the following features: regression, ulceration and / or Clark level IV-V. Results Progression developed in 114 of 503 negative SLN patients (22.7%); the first metastatic site was regional in 64% and distant in 36% of these cases. Thirty-nine patients had nodal metastases in the SLN basin as first site of progression. High-risk melanomas (P = 0.001) and elderly patients (P = 0.0005) had an increased probability of progression. Women with a higher median age and lower limbs primary melanoma developed mainly regional skin metastases, while an increased probability of distant metastases was demonstrated in patients with primary on the trunk and axillary SLN (P = 0.003, P = 0.001 respectively). Age at diagnosis, Breslow thickness and regression showed a prognostic relevance in univariate and multivariate analyses on disease-free survival and overall survival. Conclusions Even if SLN status remains the most important prognostic factor for melanoma patients, progressive disease after a negative SLNB is a relatively frequent event. However, in our opinion, only a part of negative SLNB patients with metastatic spreading should be considered as false negative (7.75%).