A 72-year-old man with a mass in his right axilla.

The patient was a 72-year-old man with a mass in his right axilla for 1 year. The tumor was painless, mobile, and slowly increasing in size; at its largest it measured 3 cm in diameter and was in a subcutaneous location. The clinical presumptive diagnosis was epidermoid cyst, mucocele, adnexial tumor, and nodule. The lesion was excised under local anesthesia. The resected specimen consisted of well-defined round and slightly fluctuant dermal nodules. Its size was 3 × 2.5 × 2 cm. The operative specimen proved to be completely cystic, and the cyst contents contained brownish serous fluid (Fig. 1). The thickness of the cyst wall was at most 0.2 cm. Histological examination revealed the absence of an epithelial lining in some areas and in some cells with apocrine-type decapitation secretion along the inner surface of the cyst wall (Fig. 2). The section showed a tumor composed of epithelial cells and connective tissue stroma, the two being intimately admixed (Fig. 3). The epithelial pattern was tubular with a double layer of lining cells, branching strands cords, and focally solid areas. Most of the stroma was of dense myxoid appearance and stained positively with PAS. Immunohistochemically, the inner cell layer of tubular structures was positive for cytokeratine, epithelial membrane antigen, and the cells of the outer cell layer were positive for vimentine and S-100. What is your diagnosis?