Favourable prognostic role of histological regression in stage III positive sentinel lymph node melanoma patients

Background: Sentinel lymph node (SLN)-positive melanoma patients are a heterogeneous group of patients with survival rates ranging from similar to 20 to over 80%. No data are reported concerning the role of histological regression on survival in stage III melanoma. Methods: The study included 365 patients with positive SLN from two distinct hospitals. The model was developed on patients from 'AOU Citta della Salute e della Scienza di Torino', and externally validated on patients from IRCCS of Candiolo. Survival analyses were carried out according to the presence of regression and adjusted for all other prognostic factors. Results: Among patients followed at 'AOU Citta della Salute e della Scienza di Torino' (n = 264), the median follow-up time to death or censoring (whatever two events occurred earlier) was 2.7 years since diagnosis (interquartile range: 1.3-5.8). In all, 79 patients died from melanoma and 11 from other causes. Histological regression (n = 43) was associated with a better prognosis (sub-HR = 0.34, CI 0.12-0.92), whereas the other factors above showed an inverse association. In the external validation, the concordance index was 0.97 at 1 year and decreased to 0.66 at 3 years and to 0.59 at 5 years. Adding histological regression in the prognostic model increased the discriminative ability to 0.75 at 3 years and to 0.62 at 5 years. Finally, using a cutoff of 20% for the risk of death led to a net re-classification improvement of 15 and 11% at 3 and 5 years after diagnosis, respectively. Conclusions: Histological regression could lead to an improvement in prognostic prediction in patients with stage III-positive SLN melanoma.