Pigmented Epithelioid Melanocytoma (Animal Types of Melanoma) on the Nose

Pigmented epithelioid melanocytoma (PEM), also known as an animal-type melanoma, is a distinctive group of melanocytic tumors with a more favorable prognosis than conventional melanoma. Since tumor-associated macrophages (TAMs) extend in the premetastatic lymph nodes in several cancers, we hypothesized that the lower rate of lymph node metastasis in PEM might be correlated with the phenotypes of TAMs. Therefore, in this report, we further investigate the subpopulation of TAMs in PEM, revealing that the main population of TAMs in histiocytic lesion is CD163+CD206+PD-L1+ M2-polarized macrophages. In addition, since the PD-L1-expressing CD205+ dendritic cells are also detected in histiocytic lesions, the PD-L1-expressing TAMs and dendritic cells might suggest favorable prognostic factors in patients with PEM.