Microcystic Adnexal Carcinoma
Key Points
Microcystic adnexal carcinoma (MAC) is a slow-growing, locally aggressive cutaneous adnexal malignancy derived from eccrine sweat glands
It occurs predominantly on the head and neck region in about 85% to 90% of cases
The etiology is unknown, but ultraviolet radiation exposure has been suggested to be a major risk factor
It generally presents as an asymptomatic, slowly growing, flesh-colored or pale yellow, solitary, indurated subcutaneous nodule, plaque, or cyst-like tumor
Perineural invasion is usually associated with a more aggressive course and a higher recurrence rate
MAC tends to be local aggressive with deep infiltration and a high recurrence rate
Complete tumor excision with histologic control of surgical margins is the treatment of choice
Recurrence rates range between 17% and 60% but distant metastases occur in less than 1%
The overall 10-year survival rate is excellent at 97.7%
Microcystic adnexal carcinoma (MAC) is a slow-growing, locally aggressive cutaneous adnexal malignancy derived from eccrine sweat glands. The appellation MAC was first applied by Goldstein, Barr, and Santa Cruz1 in 1982, based on the review of six tumors, two of which had been reported previously as sweat gland carcinomas. MAC is one of several malignant adnexal tumors, including adenoid cystic carcinoma, apocrine carcinoma, cylindrocarcinoma, digital papillary adenocarcinoma, endocrine mucin-producing sweat gland carcinoma, hidradenocarcinoma, porocarcinoma, and primary cutaneous mucinous carcinoma.2 As noted by Goldstein and coworkers, MAC “may be synonymous with previously reported cases called malignant syringoma, sweat gland carcinoma with syringomatous features, or aggressive trichofolliculoma.”1 It is a very rare tumor,3 and occurs at a reported incidence of 1.6 to 6.5 per 1,000,000 population.4
MAC occurs predominantly in the head and neck region in about 85% to 90% of cases.5,6 However, very few cases have involved the eyelids and periorbital region.7,8,9,10,11,12,13 The tumor can be highly invasive and destructive locally and can invade dermis, muscle, adipose tissue, nerves, periosteum, and bone, causing significant morbidity.14,15,16 However, regional lymph node involvement and distant metastases are rarely reported.17,18 The tumor occurs mainly in Caucasians (90%),4,19 and only seven cases have been described in patients of African descent.20,21,22,23,24,25,26 Patients usually present in the fourth to seventh decades of life, with a median age of 68 years.4 The age range is very broad, extending well into old age, but only about a dozen reported cases have been younger than 18 years, the youngest only 2 months of age.6,19,27,28
Etiology and Pathophysiology
Fewer than 700 cases of MAC have been reported in the world’s literature,3 and its rarity makes it difficult to determine its etiology. Ultraviolet exposure, ionizing radiation, and immunosuppression have all been proposed.4,30,31,32 Ultraviolet radiation exposure has been suggested to be a major risk factor for MAC.
Not only are the head and neck the most common sites for MAC, but in a large series of patients in the United States, 52% of tumors were located on the left side (driver’s side). This compared with an Australian series where the driver’s side is the right side, and 56% of MAC tumors were on the right.4 MAC has also been reported following ionizing radiation therapy with an incidence of about 10% to 19%.19,30,33 The average latency period between radiation exposure and MAC was reported to be 7 to 30 years.34
Clinical Presentation
Eyelid MAC is frequently misdiagnosed as a benign lesion or another more common skin malignancy such as squamous cell carcinoma.11 Clinically, MAC can present as eyelid swelling with surface ecchymoses (Figure 139.1A). More
commonly, they appear as an asymptomatic, slowly enlarging eyelid thickening or a flesh-colored or pale yellow, solitary, indurated subcutaneous nodule, plaque, or cyst-like tumor (Figure 139.1B). It is firm with ill-defined margins and has prominent overlying telangiectatic vessels. The surface is smooth, and ulceration is uncommon (Figure 139.1C).7,35 Pain, burning, anesthesia, and paresthesia can be seen with perineural invasion.36 The average size at presentation is usually less than 2 cm in 80% of patients; however, the absolute size may be difficult to determine due to its indistinct borders (Figure 139.1D).37 The tumor spreads by local invasion into deeper tissues early in its course38 but only rarely metastasizes to regional lymph nodes or distant sites.30,36,39,40 Orbital invasion by periocular MAC is very rare with only six cases reported.7,41,42,43,44
commonly, they appear as an asymptomatic, slowly enlarging eyelid thickening or a flesh-colored or pale yellow, solitary, indurated subcutaneous nodule, plaque, or cyst-like tumor (Figure 139.1B). It is firm with ill-defined margins and has prominent overlying telangiectatic vessels. The surface is smooth, and ulceration is uncommon (Figure 139.1C).7,35 Pain, burning, anesthesia, and paresthesia can be seen with perineural invasion.36 The average size at presentation is usually less than 2 cm in 80% of patients; however, the absolute size may be difficult to determine due to its indistinct borders (Figure 139.1D).37 The tumor spreads by local invasion into deeper tissues early in its course38 but only rarely metastasizes to regional lymph nodes or distant sites.30,36,39,40 Orbital invasion by periocular MAC is very rare with only six cases reported.7,41,42,43,44
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