Histopathologic study of recurrent Clark level II melanomas.

Overall, the prognosis for thin lesions of melanoma (less than 0.76 mm) is excellent. However, a number of melanoma patients with seemingly innocuous lesions have been reported to develop recurrences. For this reason, we examined histologic sections taken from eight cases of Clark level II melanoma that unexpectedly recurred, and compared their histopathologic features with an equal number of nonrecurrent lesions in whom reliable clinical follow-up data were available. Prognostic variables including Breslow thickness, mitotic rate, ulceration, the presence or absence of regression, a vertical growth phase component, and an associated banal nevus were evaluated in a double blind manner. When attempts were made to predict outcome based on one or more prognostic variables, the only correlation of statistical significance was the Breslow thickness (P = 0.04). A Breslow thickness greater than 0.4 mm was associated with a significantly shorter disease free interval than a thickness below 0.4 mm. There was no significant correlation between predicted outcome based on the histologic features examined and the eventual outcome based on history of recurrence (P = 0.36). These data indicate that although prognostic models that predict outcome in melanoma are generally reliable, there is a sizable population of patients with thin melanomas that do worse than would be expected.