Most of the epithelial cells on the surface, as well as those within the gland-like structures are densely pigmented . This pigment is fine to coarsely granular and is also present in some stromal cells. Cytologically all cells are benign and there are no mitoses. In a few areas the epithelium is several cells thick. Trichrome stains demonstrate that the stroma of the cores is composed primarily of fibrous connective tissue, presumably collagen.
PAS stains demonstrate a well-delineated basement membrane under most epithelial cells.
Vimentin was mostly negative, however, some cells showed faintly positive cytoplasm. HMB-45 was also positive in many of the epithelial cells. Some cells were heavily laden with melanosomes . All epithelial cells had a basal lamina and most displayed well developed desmosomes . Many cells also displayed microvilli and cilia .