A 53-year-old woman presented with a solitary lesion on her left forearm, which had first appeared approximately 20 years earlier and had gradually increased in size. Physical examination (Fig. 1) revealed a firm, reddish-brown, dome-shaped nodule, 30 9 20 mm in diameter. In addition, there were yellow-brown, circular crusts of around 1 mm in size over the lesion, along with a bleeding ulcerative area.
Histopathological findingsOn histological examination of a skin biopsy specimen, hyperkeratosis, light acanthosis and focal basaloid cell proliferation were seen in the epidermis. In the dermis, there were cystic dilated and branching tubular structures with papillary projections into the lumen, surrounded by a fibrous stroma. These ducts were surrounded by two layers of epithelial cells. The ductal cells were primarily cuboidal, but some were columnar and/or flattened. The cuboidal cells of the inner layer of the tubular structures showed decapitation secretion (Fig. 2a,b) and were positive for epithelial membrane antigen (EMA) and gross cystic disease fluid protein (GCDFP)-15 (Fig. 2c,d).