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Thin Melanomas: Going, Going, Gone?

Regression of a thin melanoma may indicate an increased risk for metastasis.

Although Breslow thickness is clearly the best predictor of metastasis in melanomas, thin melanomas sometimes metastasize. Investigators have long sought to uncover prognostic information from histologic sections that would distinguish these higher-risk thin lesions. Histologically apparent regression has been much studied as a risk factor. In this study, the authors (a panel of 10 dermatopathologists with particular expertise in the diagnosis of melanoma) compared 43 patients with primary melanomas less than 1 mm thick (mean, 0.59 mm) who developed metastatic disease and 42 patients matched for age, sex, tumor site, and Breslow thickness who did not develop metastatic disease.

The presence of extensive regression was the only significant histologic difference between the 2 groups. Regression was found in 42% of the patients who developed metastases but in only 5% of the controls. The authors defined regression fairly strictly, although they did allow for some single intraepidermal melanocytic proliferation in regressed sites. The extent of regression was assessed as less than or more than 50% of the entire melanocytic proliferation. The authors concluded that extensive regression in a thin melanoma predicts a higher likelihood of disease progression.

Comment: Regression has been evaluated as an indicator of prognosis for many years with conflicting results, probably resulting from differing definitions of regression. Although the authors attempted to define specific criteria for determining the presence and extent of regression, the criteria remain vague, and the results may not be reproducible outside the study setting. Nonetheless, these findings add to the growing evidence that extensive regression in an otherwise low-risk melanoma is cause for concern. Whether sentinel lymph node biopsy is warranted for patients with these lesions is grounds for a follow-up study.

— Bruce R. Smoller, MD

Published in Journal Watch Dermatology June 26, 2002

Citation(s):

Guitart J et al. Histological characteristics of metastasizing thin melanomas: A case-control study of 43 cases. Arch Dermatol 2002 May; 138:603-8.

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