Using a continuous transformation of the Breslow thickness for prognosis in cutaneous melanoma

Although the Breslow thickness provides the most important histologic information for prognosis in cutaneous melanoma, controversies and uncertainty remain about how best to use thickness. It is unclear whether cut points should be used, or, if they are used, which are optimal. We studied new data collected from more than 1,000 patients followed up for a relatively long period. From Cox proportional hazards models of survival we learned that more cut points provide more prognostic information than using, for example, just 1 cut point at 1.7 mm. Nevertheless, a continuous transformation provides an effective alternative that captures the information that thickness provides, and it avoids the pitfalls of using multiple cut points. In a multivariate model, this transformation provided strong prognostic information, and the result produced a prognostic score for cutaneous melanoma. This score provides a practical way that Cox model results can be used, and we believe it consolidates the prognostic information provided by traditional histologic and clinical variables. When newer prognostic variables are introduced, we suggest that they be used with this continuous transformation of thickness rather than with cut points in thickness.