Melanoacanthoma. Ultrastructural and immunological studies.

Electronmicroscopic studies confirmed that melanoacanthoma is a non-nevoid elevated epithelial tumor composed of keratinocytes of both basaloid and spinous differentiation and of large dentritic melanocytes. The block in transfer of pigment from melanocytes to keratinocytes was found not to be complete. Langerhans cells, present in the malpighian layers were normal in morphology. Immunofluorescent studies and an immunoprecipitin assay also showed our patient's melanoacanthoma not to be related to malignant melanoma.