Microcystic Adnexal Carcinoma - Submitted on: Tuesday October, 23, 2001

Contributed by:Artur Zembowicz, MD, Stephen Wang, MD

Microscystic adanexal carcinoma (MAC) is a rare cutaneous neoplasm first desdribd by Goldstein DJ et al. in 1982. Before, similar cases had been referred to as malignant syringoma, sweat glands carcionma with syringomatous features, or aggressive trichofolliculoma.

Definition: MAC is a locally invasive eccrine neoplasm showing basaloid, epidermoid and ductal differentiation. It diffusely into deep dermis and subcutaneous tissue and is invariably associated with a desmoplastic stroma. Perineural invasion and involvement of the subcutis and skeletal muscle are common features.

Clinical Features: MAC occurs mainly in adults with a median age of onset in the fourth decade. It has equal sex distribution. Seventy three percent of cases occur in Caucasians. The tumor is localized almost exclusively on the neck and head: the upper and lower lips are the most common sites. Other common sites include eyebrow, cheek, nose, scalp and chin. Clinically, the lesion is a pale yellow, firm and indurated papule or plaque measuring from 0.25 to 2.5 cm, and the lesion often has ill-defined border and overlying telangiectasia. Desmoplastic sclerosing basal-cell carcinoma is the most common clinical diagnosis. Because of perineural invasion associated with MAC, patients may have local neurologic complaints, such as pain, burning, stinging, anesthesia or paresthesia, in the involved area.

Histology: Figures (Click on an image for a larger view) Figure 1 Figure 2 Figure 3 MAC is a poorly circumscribed, asymmetrical, and highly infiltrative dermal tumor that may extend to the subcutis and skeletal muscle. Two components of the tumor can be appreciated. First, in some areas of the tumor, strands or islands of basaloid keratinocytes predominate. These strands of keratinocytes are often compressed by the surrounding desmoplastic stroma, and the keratincytes have little cytologic atypia (Figure 1). In the papillary dermis, some of the keratinocytes may contain abortive hair follicles and horn cysts, with or without calicification (Figure 1). The deeper component of the tumor shows ductal differentiation frequently lined by two layers of cuboidal cells (Figure 2). Again, there is little cytologic atypia and mitotic figures may be rare. Perineural involvement is frequent (Figure 3). Involvement of the skeletal muscle and bone can also occur.

Treatment: Wide local excision and Mohs micrographic surgery are the current standard therapeutic modalities. However, because of the propensity of MAC for perineural invasion, the recurrence rate is high. Mohs technique may allow the surgeon to extend the excision until the perineural extensions that remained after the initial resection are totally removed.

Bibliography: Goldstein DJ, Barr RJ, Santa Cruz DJ. Microcystic adnexal carcinoma. A distinct clinical pathological entity. Cancer 50;566-572. LeBoit PE, Sexton M. Microcystic adnexal carcinoma of the skin: a reappraisal of the differentiation and differential diagnosis of an under-recognized neoplasm. J. Am Acad Dermatol. 1993;29:609-618. Sebastien TS, Nelson BR, Lowe L et al. Microcystic adnexal carcinoma. J Am Acad Dermatol. 1993;29:840-845. Weedon D, Skin Pathology. (1998)Churchill Livingstone, p. 743-744. Kirkham N. Tumors and cysts of the epidermis. In: Elder D, Elenitsas R, Jaworsky C, et al. eds Lever's Histopathology of the skin. 8th ed. Philadelphia: Lippincot-Raven Publishers. pgs. 792-793.

 

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