Microcystic Adnexal Carcinoma
David Cassarino, MD, PhD
Key Facts
Terminology
Microcystic adnexal carcinoma (MAC)
Synonyms: Sclerosing sweat duct carcinoma, syringoid carcinoma
Low-grade malignant adnexal tumor with follicular and ductal differentiation
Clinical Issues
Most common on the face
Indurated, plaque-like lesion
Mohs excision is effective and likely the optimal approach in most cases
High incidence of local recurrence, but only very rare metastases
Microscopic Pathology
Bland-appearing dermal-based adnexal tumor
Deeply invasive and not well-circumscribed
Perineural invasion often present in deeper areas
Superficially, typically consists of folliculocystic elements
Deeply, consists of infiltrative cords and ductal structures lined by bland-appearing cells
Lymph nodes only very rarely involved and likely represent local, deep invasion
Ancillary Tests
Low proliferative rate by Ki-67 (high in BCC)
Low levels of p53 and Bcl-2 (high in BCC)
Top Differential Diagnoses
Desmoplastic trichoepithelioma
Syringoma
Desmoplastic basal cell carcinoma
 Scanning magnification of a microcystic adnexal carcinoma shows a diffusely infiltrative neoplasm in the dermis and extending into the dermal-subcutaneous interface  . |
 High magnification of MAC shows the relatively bland-appearing cells forming small cords in a desmoplastic stroma. Note the focal perineural invasion  . |
TERMINOLOGY
Abbreviations
Microcystic adnexal carcinoma (MAC)
Synonyms
Sclerosing sweat duct carcinoma
Syringoid carcinoma, malignant syringoma (older terms, should be avoided)
Definitions
Low-grade malignant adnexal tumor with follicular and ductal differentiation
ETIOLOGY/PATHOGENESIS
Environmental Exposure
Some cases may be related to solar damage (UV radiation) or radiation therapy
Higher incidence reported on left side of face, which receives greater solar exposure during driving
Unknown
Most cases
CLINICAL ISSUES
Epidemiology
Incidence
Uncommon adnexal tumors
Age
Usually occur in middle-aged to older adults
Gender
Slightly greater in females
Site
Most common on the face
Upper lip is most common site
Can also occur on scalp, trunk, extremities, axillae, and groin
Presentation
Indurated, plaque-like, or nodular lesion
Treatment
Surgical approaches
Complete excision with clear margins
Mohs excision is effective and likely the optimal approach in most cases
Adjuvant therapy
Reports of effectiveness with adjuvant radiotherapy
Prognosis
High incidence of local recurrence (up to 50%), but only very rare metastases
Metastases have been reported to local lymph nodes but may represent local, deep invasion, rather than true metastasis
MACROSCOPIC FEATURES
