Thin level IV malignant melanoma. A subset in which level is the major prognostic indicator.

A small proportion of "thin" malignant melanomas will metastasize and cause death. To assess the role of discordance between the major indicators of tumor depth (thickness and level) as a possible explanation for this phenomenon, prognosis by level has been examined in 255 cases, with tumors ranging in thickness from 0.6 to 1.1 mm. This is the range of thickness at which levels II, III, and IV overlap. The 5-year survival rate of patients with level IV tumors in this thickness range (59.35%) was poor (p less than 0.0001), relative to that of patients with level II (96.8%) and III (94.49%) lesions in the same range of tumor thickness. The distributions of other major prognostic indicators, among the groups of patients with tumors at each level, were examined to assess the possible contribution of factors other than level to the differences in survival between the three groups. These differences in survival could not be attributed to differing distributions of tumor thickness, tumor location, or patient sex. Of six prognostic variables, examined by Cox multivariate regression analysis, for tumors of thickness 0.6 to 1.1 mm, only level was found to have independent prognostic significance (p = 0.0025). The thin level IV melanoma appears to be an important exception to the rule that this melanomas are associated with an excellent prognosis. In this, as well as in other studies, after accounting for the effect on prognosis of tumor thickness, level has been shown to be a prognostic indicator with independent significance. The continued use of level as a prognostic indicator, in addition to thickness, is recommended.