Breslow thickness and Clark level in melanoma - Support for including level in pathology reports and in American Joint Committee on Cancer staging

BACKGROUND, Thickness is known to be an important survival prognosticator f or cutaneous melanoma, but controversy exists as to whether Clark level of invasion retains prognostic significance once thickness has been accounted for. A recent proposal to eliminate Clark level from the staging system for melanoma of the American Joint Committee on Cancer (AJCC) prompted the aut hors to investigate whether level adds useful prognostic information to Bre slow thickness. They used the data base of the New York University Melanoma Cooperative Group (NYUMCG) Registry. METHODS. The analysis was based on 919 patients with AJCC Stage I or II mel anomas diagnosed between 1972 and 1982 and followed for an average of 10.9 years. Melanoma thicknesses were divided into 4 categories (less than or eq ual to 0.75, 0.76-1.50, 1.51-4.00, and >4.00 mm), Patients were cross-class ified according to tumor thickness and Clark level (II-V). For each combina tion of thickness and level, the Kaplan-Meier survival curve and 10-year su rvival proportion were computed, using death from melanoma as the outcome. The impact of Clark level on survival was evaluated for each of the thickne ss categories. The Cox proportional hazards model was used to assess the si multaneous effect of thickness and level on survival while controlling for other important prognostic factors, i.e., age, tumor location, and presence or absence of ulceration. RESULTS. Level of invasion was a significant predictor of death from melano ma in each of the four thickness categories. Likewise, in the Cox analyses, level was a significant prognostic variable, even after thickness was incl uded in the model and regardless of whether thickness was treated as a cate goric or a continuous variable. CONCLUSIONS. These results confirm that both tumor thickness and level of i nvasion are important independent prognostic factors in AJCC Stage I and II melanomas. The authors recommend that Clark levels be kept as criteria in the AJCC staging system and be included in pathology reports. [See editoria l on pages 491-6, this issue.] (C) 2000 American Cancer Society.