"Thin" malignant melanoma: risk factors and clinical management.

Thin melanomas can metastasize and can be lethal. Six hundred eighty-one patients with melanomas less than 0.76 mm thick have been evaluated, and are reviewed in this study and discussed in the context of a literature review. Among those referred without metastatic disease (583 patients), 4.8% metastasized after a mean follow-up of 3.6 years. Among those referred with metastatic disease (98 patients), mortality was 35% after a mean follow-up of 5.9 years. Male patients (p less than 0.04) and patients with axial primary lesions (p less than 0.05) had increased risk of metastasis. Severe histological regression was present in 40% of primary lesions that metastasized and only 17% of similar lesions that did not (p less than 0.001). Increased age was associated with increased local skin metastases, but not with increased nodal or distant metastases. A prognostic model was designed that identifies a low-risk population with an actuarial risk of metastasis at 10 years that is less than 3%. High-risk patients have an actuarial risk of metastasis of 11% at 5 years and 22% at 10 years (p = 0.0084). Identifying high-risk and low-risk patients with thin melanomas may improve guidelines for the application of adjuvant therapies to this population. New approaches to this problem include use of molecular biology techniques, immunohistochemistry, and varied methods of histological sectioning.