Abstract
Melanoacanthoma is a rare benign mixed tumor of both keratinocytes and melanocytes. Although some authors said that it is a rare variant of seborrheic keratosis, it has clinical and histological features distinct from seborrheic keratosis. It has large dendritic melanin-laden melanocytes throughout all levels of epidermis showing a disruption of melanin transfer from the melanocytes to neighboring keratinocytes. However, it is difficult to distinguish melanocytes clearly from cutaneous pigment in immunohistochemical stain with usually used brown chromogen. We used chromogen with brick-red indicator product (VECTOR® NovaRED™) in S-100 and melan-A immunohistochemical staining to distinguish melanocytes from melanin laden keratinocytes. We suggest that the immunohistochemical staining using this novel chromogen may be useful in the diagnosis of melanoacanthoma.