Enhancing the prognostic role of melanoma sentinel lymph nodes through microscopic tumour burden characterization: clinical usefulness in patients who do not undergo complete lymph node dissection

This study aimed to investigate the sentinel lymph node (SLN) tumour burden to predict the non-SLN positivity rate and the survival of melanoma patients to evaluate whether SLN microstaging could predict the prognosis, similar to what is currently performed by examining the lymph nodes excised by complete lymph node dissection. Of 1130 consecutive melanoma patients who underwent SLN biopsy, 226 were tumour-positive and 204 were included in this study. SLN metastases were classified on the basis of dimensional (Rotterdam) and topographic (Dewar) criteria either separately or combined. SLN metastases more than 1 mm in diameter had the highest non-SLN positivity rate (31%) compared with metastases 0.1-1 mm (10%) and less than 0.1 mm (4%). The non-SLN positivity rate was 45% for extensive metastases, 5% for subcapsular metastases and 23-29% for parenchymal, combined and multifocal classes, therefore suggesting a simplification of the parenchymal SLN metastases into only two classes: extensive and 'not extensive'. The dimension of the metastasis was correlated with a different non-SLN positivity rate only when the metastasis was in the parenchyma (20-36%) and not when it was in the subcapsular location (4-7%). Interestingly, the 5-year melanoma-specific survival (MSS) was 89% for patients with subcapsular less than 0.1 mm metastases and 45% for patients with nonsubcapsular more than 1 mm metastases (P=0.017). In the parenchyma, larger metastases (1 mm) were related to a lower 5-year MSS (46%) than smaller (1 mm) metastases (MSS 77%). SLN tumour burden characterization can be simplified and it can provide prognostic information on non-SLN positivity and survival, which is especially useful in patients who do not undergo complete lymph node dissection.