What is the behavior of Breslow’s thickness?

Abstract

9097 Background: Localized cutaneous melanomas (CM) have their clinical course predicted by microscopic findings in the tumor specimen, mostly Breslow’s thickness (BTL), ulceration and mitoses. It is not certain whether BTL has a linear relationship with overall survival (OS) or relapse-free survival (RFS). The aim of this study was to evaluate BTL´s linear (LC) and its non-linear component (NLC) with relation to survival. Methods: All consecutive cases of CM treated from 1997 to 2006 at a single institution were identified, individuals with stage I or II tumors, minimum follow up of one month and known BTL were selected, socio-demographic data, clinical and pathological findings, treatment and outcomes were abstracted. Information about ulceration was missing in more that 30% of cases and it was not evaluated, there was no information about mitotic rate. Survival was estimated by the Kaplan-Meier method. Multivariate analyses were performed by the Cox model. BTL was evaluated as a continuous variable, and the LC and NLC by the technique of smoothing, using p-splines. Results: There were 1465 cases of CM, 51 with no follow up, 137 had no information about BTL and 202 had advanced stages. This analysis is based on 1075 cases. In the Cox model, the variables associated OS were age [hazard ratio (HR) 1.02, 95% CI 1.01 to 1.03], sex (HR 1.56, 95% CI 1.2 to 2.04) and BTL (HR=1.079, 95% CI 1.065 to 1.094). The variables associated with RFS were age (HR 1.017, 95% CI 1.009 to 1.024), sex (HR 1.372, 95% CI 1.104 to 1.704) and BTL (1.068, 95% CI 1.057 to 1.080). In the analysis of LC and NLC of BTL, it was found that both LC and NLC were statistically significant for OS and RFS. There was an increase in the HR as BTL increased in those lesions thinner than 4mm, then such increase was not as evident and lesions with more than 10mm had a similar OS and RFS (plateau). Conclusions: BTL is one of the most powerful prognostic criteria of patients with stage I and II CM. The risk of death increases linearly for thin lesions up to 4mm, lesions thicker than 10mm behave as a uniform group with no further decrease in OS or RFS as the lesion becomes larger. In conclusion, BTL may not behave as a linear function, it has a LC for thinner lesions, but for thicker lesions, above 10mm, further increase in BTL may add no more risk.