Biologic behavior of thin malignant melanomas with regressive changes.

Thin cutaneous malignant melanomas are defined as lesions measuring less than 0.76 mm in maximal thickness. Eight of the 36 thin lesions that we studied metastasized within two to 120 months. Of the 11 lesions with regressive features, five (45.5%) metastasized. Of 25 lesions without regression, only three (12%) metastasized. Thin melanomas with regressive changes need to be reported as a separate category because of their propensity to metastasize. Conventional prognostic guidelines for treatment of thin melanomas are not applicable to this type of lesion. Clinicians need to be cognizant that regressive changes are serious warning signals when they occur in thin melanomas.