Microcystic Adnexal Carcinoma: An Often Misdiagnosed, Locally Aggressive Growing Skin Tumor

Abstract

Microcystic adnexal carcinoma (MAC) belongs to the spectrum of locally aggressive adnexal carcinomas and most commonly occurs in the head and neck region. Recently it has been proposed that MAC is an apocrine tumor. It is characterized by slow, but locally aggressive growth with infiltration of subcutaneous fat tissue, muscles, perichondrium, periosteum, or perineurium. As a result, surgical treatment often leads to ablation defects, which are many times the size of the clinical lesion. In 1982, Goldstein and colleagues first reported MAC to be a distinct histologic entity characterized by a combination of keratinous cysts in the upper dermis, islands and strands of small basaloid, benign-appearing keratinocytes or squamous cells in the deeper dermis within a dense desmoplastic stroma, and areas of ductular differentiation. The authors report the case of a 78-year-old woman in whom a diagnosis of MAC was made when a tumor on the right cheek recurred for the second time. Previous histopathologic diagnoses were squamous cell carcinoma and desmoplastic trichoepithelioma. Local recurrences of the tumor occurred, despite histographic surgery because in hematoxylin and eosin stains, small islands of the deceptively benign-appearing small basaloid cells of MAC were not recognized as tumor cells. The reported case demonstrates the difficulties in diagnosing MAC and indicates that MAC should always be considered in the differential diagnosis of slowly growing tumors in the head and neck region. If MAC is diagnosed too late, it can be inoperable because of its infiltrative growth.

Skin adnexal neoplasms—part 2: An approach to tumours of cutaneous sweat glands

“…Histologically, an in situ component in the form of epithelial islands bounded by a myoepithelial layer, and highlighted by CK 5/6, p53, calponin and SMA, is frequently present in PCMC in comparison to metastatic mucinous carcinoma. 78 In comparison, breast mucinous carcinoma metastatic to the skin mostly presents with lesions on chest wall, breast and axillae, and these locations can serve as clue to the breast origin. In addition, these metastatic lesions lack an in situ component histologically.…”

Microcystic Adnexal Carcinoma

“…6 The gold standard in achieving definitive treatment is Mohs micrographic surgery. 2,3,7 The incidence of local recurrence peaks 2 years subsequent to surgery. Snow et al reported an 89% success rate of Mohs surgery with a 2 year follow-up.…”

“…5 Local and distant metastases have been reported. 3,5,7 Patients must be closely monitored for several years following resection as the overall recurrence rate of MAC is quite high. 5 The major histologic differential diagnosis of MAC is syringoma, a difference that cannot be determined in superficial specimens.…”

“…7 Histologically, desmoplastic TE is similar to MAC, with narrow strands of tumor cells admixed with numerous keratocysts set in a desmoplastic stroma (Fig. 4).…”

“…Superficial biopsies that contain keratinous cysts and/or "tadpole-like" tumor strands are inadequate and have the potential to lead to the misdiagnosis of MAC as a syringoma or TA. 2,7 Although MAC has similar histologic features to the aforementioned neoplasms it destructively infiltrates the deep dermis, subcutaneous, and neural tissue, emphasizing the need for a deep biopsy. Pathologists are discouraged from succumbing to the pressure of making a definitive diagnosis in the presence of a superficial specimen.…”