EP140 - A case of Microcystic Adnexal Carcinoma identified in the perianal region

Image or Table (Do Not add text here):

Purpose/Background: Microcystic adnexal carcinoma (MAC) is a cutaneous neoplasm most often found in the head and neck. Otherwise referred to as sclerosing sweat duct carcinoma, it is a locally aggressive carcinoma with high local recurrence rates. Uncommon sites include the axilla, trunk, extremities and genitalia. In this case, we describe the incidence of MAC in the perianal region.

Methods/Interventions: A 57-year-old female was referred for ‘possible lipoma’ to the right perianal area. It was first noted thirty years prior with recent growth and no associated symptoms. The patient had no known medical or surgical history but endorsed an 80-pack-year smoking history. Physical examination revealed a three centimeter right-sided dermal mass on the right buttock with no signs of fistula or infection. The patient underwent excisional biopsy of the right buttock mass with total excision site measuring 9 x 3 centimeters. Surgical pathology revealed MAC with tumor at the superior, inferior, deep resection margins, at < 1.0 mm from the medial margin and the lateral margin free of carcinoma. No angiolymphatic or perineural invasion was identified. The case was presented at institutional tumor board and she was scheduled for re-excision for clean margins. Re-excision margins were negative for carcinoma on surgical pathology.

Results/Outcomes: N/A

Conclusion/Discussion: MAC, also referred to as malignant syringoma or sweat gland carcinoma with syringomatous features, is a rare slow-growing cutaneous neoplasm. It is often asymptomatic presenting as an indurated skin-colored nodule, papule or plaque accounting for less than 1% of skin carcinomas. MAC has been reported to have a higher female predilection most common in the sixth decade. Risk factors include prior radiation, immunosuppressed states and UV exposure. It is described as a locally aggressive neoplasm presenting with glandular and follicular differentiation with proclivity for perineural invasion. Adverse prognostic factors include perineural invasion, regional lymph node involvement, visceral metastases and tumor recurrence. Few reports have described perianal locations with most describing vulvar MAC.
Histologic characteristics include features of both eccrine and follicular differentiation with lamellar keratin-filled pseudohorn cysts demonstrating nests and cords resembling ductal structures. Immunohistochemistry can assist in differentiating MAC from other tumors with positive Keratin and Ductal lumina immunostains. Skin biopsy with adequate tissue depth is required for diagnosis using punch, incisional or excisional biopsy based on localization. Treatment requires surgical excision with wide local excision or Mohs micrographic surgery given its infiltrative nature. Radiotherapy (RT) has been described for lesions not amenable to surgical excision or at high risk of local recurrence. However, use of RT alone is not recommended due to inefficacy in treatment and association with clinically aggressive transformation. Reports describe the use of neoadjuvant RT for potential morphologic changes or reductions in neoplastic volume prior to excision for areas requiring tissue conservation. Imaging is not routinely recommended, nor is metastatic work-up given low propensity for distant metastases. Surveillance is recommended every six to twelve months for the first five years post treatment with recurrence rates described as high as 60%.