Papillary eccrine adenoma: immunohistochemical study and literature review.

A case of papillary eccrine adenoma on the right forearm of a 78-year-old Japanese woman is reported. The tumor was 1.3 cm in diameter, occupying the whole thickness of the dermis. Histologically, the tumor was composed of dilated tubules of various sizes with intraluminal papillary projections, and was surrounded by a fibrous stroma. An immunohistochemical study revealed that the proliferating tubules were composed of a single outermost layer of alpha-smooth muscle actin- and keratin 14-positive myoepithelial cells, and keratin 8-positive inner cells. This antigen expression pattern was comparable to that of the normal eccrine secretory coil, which indicates that the tumor differentiated toward the secretory coil of an eccrine sweat gland.