The pathogenesis and prognostic implications of regression in
melanoma are not well understood. It has traditionally been considered an immunologically mediated phenomenon. Improvement in the knowledge of the mechanisms that lead to regression may prove to be of great value in an era in which treatments oriented to the augmentation of the host's immunity against
melanoma have demonstrated excellent clinical results. This study was designed to improve the understanding of the mechanisms underlying
melanoma regression and the differences between similar situations in benign
melanocytic nevus. The study sample consisted of 77 lesions: 62
melanomas and 15
halo nevi. The following markers were included in the study: CD4, CD8, FoxP3, PD1, CD123,
granzyme, and TIA-1. Staining was evaluated in 5 categories, according to the percentage of labeled cells.
Granzyme, PD1, and TIA-1 stained significantly more cells in
halo nevi than in
melanomas with regression (P < 0.01). The ratio CD123/TIA-1 was higher in
melanomas than in
halo nevi (1 vs. 0.67, P < 0.05). Regression in the 62
melanomas was categorized as early in 14 cases and late in 48 cases. Early regression was associated with a higher percentage of CD123, CD4, and TIA-1 staining than late regression. The inflammatory infiltrate found in
halo nevi is characterized by a higher number of active cytotoxic T cells and regulatory PD1-positive T cells than the infiltrate found in
melanoma with regression. CD123 staining was higher in early regression than in late regression, suggesting the presence of a tolerogenic mechanism in this phenomenon's initiation phase.