Thin melanoma

The incidence of malignant melanoma is increasing and a preponderance of the melanomas diagnosed today are "thin in terms of Breslow criteria. Although thin melanomas, as a group, are associated with a very good prognosis, a subset of these tumors may metastasize and cause death. These cases can be identified by using prognostic models, including the "standard" American Joint Committee on Cancer criteria, and other attributes identified in follow-up studies.

To review the history of concepts of prognostic modeling in melanoma, focusing on thin melanomas.

Selected literature.

About 40 years ago, it was realized that malignant melanoma, once almost uniformly fatal, could be divided into categories with better or worse prognosis through the use of prognostic models. The first simple models, Clark levels of invasion and Breslow thickness, are still in use. Thickness remains the single most useful variable. Breslow recognized that melanomas less than 0.76 mm in thickness were associated with a very good prognosis, with no metastases in his limited initial study. The American Joint Committee on Cancer selected a cutoff of 1.0 mm, which achieves a similar result, with stage modifiers, although some metastases and deaths do occur with stage I lesions. Clark demonstrated an almost equally good prognosis for his level II invasive melanomas and recognized that most of these lesions, although invasive, lacked the ability to form tumors or to undergo mitosis in the dermis and were therefore "nontumorigenic" and "nonmitogenic" and lacked competence for metastasis. Studies of these low-risk melanomas have led to the development of criteria for earlier diagnosis and a steady, but still inadequate, improvement in prognosis for melanoma overall. Multivariable models currently can identify groups of patients within the "thin melanoma" category whose prognosis varies, from a disease-free survival of close to 100% to about 70%. Prognosis declines more or less linearly with increasing thickness, modified by ulceration, mitotic rate, and other attributes.