The tumor is described as firm, slowly growing and poorly circumscribed. It tends to occur in older adults.
The histologic features are similar to adenoid cystic carcinomas arising in the salivary glands. Perineural invasion can often be found in larger tumors. Immunohistochemical stains are positive for cytokeratins, EMA, S100 (focal) and polyclonal CEA.
The diagnosis requires exclusion of:
(1) a metastasis from an adenoid cystic carcinoma elsewhere.
(2) an adenoid basal cell carcinoma
(3) mucinous carcinoma of the skin
(4) primary cribriform apocrine carcinoma
The prognosis is very good if:
(1) the tumor is arising on the head (scalp, etc)
(2) the tumor has been completely excised (negative surgical margins)
(3) there are no large nerves with perineural invasion near a margin
(4) there are no metastases (to lymph nodes, lung, etc)
Recurrences are relatively common, especially if the original resection was inadequate.
