Microcystic Adnexal Carcinoma

Elizabeth Delshad, BS; Désirée Ratner, MD


Skinmed. 2004;3(6) 

A 71-year-old woman presented with a firm flesh-colored plaque with overlying whitish discoloration that had been present on her left cheek for at least 15 years (Figure 1). The lesion measured 1.6x1.1 cm in diameter. The patient had a history of radiation treatment for acne. What is your diagnosis? What should be the course of management?

Preoperative view of microcystic adnexal carcinoma on the left medial cheek.

Microcystic adnexal carcinoma (MAC), also known as sclerosing sweat duct carcinoma, is a rare malignant tumor that demonstrates follicular and eccrine differ-entiation.[1] It is frequently misdiagnosed both clinically and histologically, often resulting in inadequate treatment and a high rate of recur-rence.[2,3] Awareness of this tumor is critical because of its locally invasive character and high morbidity, despite its benign clinical and histologic appearance.

Clinically, the classic presentation is that of a slowly growing indurated plaque, nodule, or cyst that has usually been present for many years.[4] It is typically firm and pale yellow with overlying telangiectasias.[1] The average size at presentation is 2 cm.[4] MAC occurs mostly on the head and neck, with a propensity for the left side, although the etiology of this left-sided tendency has not yet been formally studied.[2,5] These tumors are usually asymptomatic and often ignored for many years.[4] Perineural invasion, which is common, may manifest as symptoms of numbness, burning, anesthesia, or paresthesia, but is more often asymptomatic.[4] The clinical differential diagnosis includes morpheaform basal cell carcinoma, infiltrative squamous cell carcinoma, cyst, scar, and other adnexal tumors.[2,4] The patient's history should be surveyed for possible risk factors, including a history of radiation therapy and ultraviolet exposure.[5]

MAC histology is actually very bland, rarely displaying cellular atypia, mitotic figures, or necrosis, which accounts for its frequent histologic misdiagnosis.[3,4] Characteristically, this tumor exhibits keratin-filled cysts, ductal structures in a desmoplastic stroma, and nests and cords of basaloid cells invading the deep dermis to the subcutaneous fat.[4,5] The histologic differential diagnosis includes trichoadenoma, syringoma, desmoplastic trichoepithelioma, syringoid eccrine carcinoma, adenosquamous carcinoma, squamous cell carcinoma, morpheaform basal cell carcinoma, and even metastatic breast carcinoma.[3,4] Often a superficial punch or shave biopsy is too small to contain the architectural features necessary for diagnosis, necessitating an incisional biopsy to obtain a larger specimen.[3] The importance of an adequate deep biopsy specimen cannot be overemphasized because deep infiltration distinguishes MAC from other similar tumors and can reveal margins with perineural involvement.[4,5] Light microscopy remains the gold standard for diagnosis.[5]

In this case a punch biopsy was performed, revealing small duct-like structures and aggregates infiltrating the entire thickness of the dermis, consistent with a diagnosis of MAC.

MAC is a locally aggressive tumor, which invades adjacent tissue by expansion, infiltration, perineural invasion in a pipeline fashion, and shelving and skating along fascial planes, accounting for subclinical tumor invasion several centimeters beyond the clinically visible margins.[1] Rare lymph node metastases have been reported, and only two cases of distant metastases have been described.[1,6] Its slow and relentless invasion can also involve the subcutaneous tissue, muscle, and bone.[7] CT and MRI have been used to detect extensive invasion by these tumors to allow preoperative localization of the extent of tumor invasion.[4]

MAC carries an overall 10-year recurrence rate of 18%.[2] Most recurrences happen within 2 years of treatment but may occur even several decades later.[8] The recurrence rate of MAC increases as tumor size increases.[5]

Treatment with Mohs micrographic surgery is considered first-line therapy for MAC, even though the overall recurrence rates between Mohs and simple excision are not significantly different.[2] Mohs surgery is preferred because the tumor is cleared generally within a single operative day, the defect sizes are the same as or smaller than those obtained following simple excision, microscopic evaluation of the entire peripheral and deep margin of the surgical specimen is performed, and the short-term recurrence rates are lower.[2,5] Radiation therapy is considered ineffective because MAC is generally radioresistant, with a recurrence of most tumors post-treatment.[1,9] Careful preoperative counseling should prepare the patient for the possibility of a large surgical defect, since the average defect is 4 times the size of the clinically apparent lesion.[2,7] The dermatologic surgeon may wish to consult with a multidisciplinary team of surgical specialists if the tumor is sufficiently invasive that parotidectomy, temporal bone resection, or other extensive surgery could be required.[7,8] Although the goal of treatment is to achieve tumor-free margins, debulking the tumor has been described as an option for patients whose resections could carry a significant risk of mortality, such as tumors that extend into the skull base.[6]

The overall recurrence rate of MAC is high, and the possibility of recurrence exists even decades after resection. A study based on long-term follow-up suggests that all patients, irrespective of the method of treatment or the status of their margins, should be monitored closely for tumor recurrence over several decades.[7] Patient visits should be scheduled every 6 months to 1 year, and sooner if new or changing lesions are noted adjacent to or within the surgical site.

Given the high-risk location and ill-defined borders of the lesion as well as the locally aggressive nature of MAC, the decision was made to treat this patient with Mohs micrographic surgery. Histopathologic evaluation revealed perineural invasion. It took two stages of excision to reach a tumor-free plane. The resulting defect measured 1.8x2.6 cm and extended to the level of the muscularis (Figure 2). The defect was closed primarily, with a final wound length of 7.3 cm. No further treatment was required; the patient will be followed regularly on a twice-yearly basis to monitor for recurrence.

Final defect after Mohs micrographic surgery.