A case of
Bednar tumor on the right shoulder of a 47-year-old Japanese woman is reported. Histological examination showed plump, spindle cells arranged in a storiform pattern in central areas of the
tumor and a diffuse infiltration of the dermal stroma, which was frequently extended into the subcutis at the periphery of the
tumor. The
tumor contained a fairly identified population of dendritic pigmented cells. Ultrastructurally, most cells had folded nuclei, were spindle-shaped and had long, slender cytoplasmic projections. Dendritic pigmented cells, which were dispersed among neoplastic cells, contained premelanosomes and mature melanosomes. Immunohistochemically,
tumor cells exhibited positive reactions for
vimentin and CD 34 and failed to show a positive reaction for
neuron specific enolase, HMB-45 or
S-100 protein.
Factor X IIIa was only expressed on
tumor cells around
melanin-containing cells, which reacted positively with
antibodies to
S-100 protein and
vimentin. These results indicate that the phenotype of
tumor cells around
melanin-containing cells differs from other
tumor cells and that this difference may be caused by the relationship of
tumor cells and
melanin-containing cells.