Identification of higher risk thin melanomas should be based on Breslow depth not Clark level IV

BACKGROUND, There is good prognostic correlation for the two microstaging s ystems, Breslow depth and Clark level, commonly used to stage melanomas. Ma ny investigators have reported that Breslow depth is the superior microstag ing method. Although Clark level has been dropped from most of the proposed American Joint Committee on Cancer (AJCC) melanoma staging system, the AJC C system still includes Clark Level IV as a criterion for upstaging thin me lanomas. The authors sought to determine whether this is appropriate, based on melanoma patient data in the Duke Comprehensive Cancer Center database. METHODS. Of the 8833 patients registered between January 1, 1970 and Decemb er 31, 1995, complete data on Breslow depth and Clark level was available f or 4560 patients who were without nodal or metastatic disease at presentati on. Ten-year survival was measured from the date of excision of the primary tumor until death from melanoma and analyzed using Kaplan-Meier and Cox pr oportional hazard methodologies. RESULTS, When analyzed separately, both increased Breslow thickness and Cla rk level correlated with shorter survival times. During subgroup analysis, Breslow thickness remained a significant prognostic indicator of survival a t Clark Levels III and IV. Conversely, at narrow levels of Breslow thicknes s (i.e., 0-0.75 mm, > 0.75 -1.0 mm, > 1.0-1.5 mm) survival times were indis tinguishable between Clark Levels III and IV. For the broader Breslow thick ness interval of 0-1.0 mm, a barely significant difference between Clark Le vels III and TV could be obtained. However, for this thickness range, even greater differences in survival could be obtained by merely comparing Bresl ow subgroups (i.e., less than or equal to 0.8 mm vs. > 0.8-1.0 mm, less tha n or equal to 0.9 mm vs. > 0.9-1.0 mm). CONCLUSION, The authors' data suggested that, after controlling for Breslow depth, Clark level was not a good prognostic indicator for survival. If th e AJCC's objective is to design a classification system that will reliably predict the higher risk melanomas, then the system should be based on tumor thickness, which is clearly a better prognostic indicator, and should not be modified because of Clark level. (C) 2001 American Cancer Society.