Lesions revealing regressive structures

Histological regression phenomena have been described in both benign and malignant lesions.1-5 Regression of benign nevi can occur spontaneously or after repeated trauma, and has an incidence of 1% in the general population.6,7 Spontaneous regression of melanomas occurs with an estimated prevalence of 10%–35%.1-5 The exact significance of regression phenomena is a matter of continuous debate.8,9 Recent studies analyzing cases of regressing melanoma suggest a favorable prognostic role of regression, possibly due to a host immunological response to the tumor.9 This phenomenon therefore could reflect the role of the immunologic system against the primary tumor; thus, its presence should be considered prognostically favorable. However, the prognostic value of extensive regression has been described by some authors as a worsening factor in melanoma.