Clinical features

• 6-90 years (4^th-7^th decade), M=F
• Caucasians ++
• Nasolabial & periorbital regions
• Slowly growing firm 0.5-2.0 cm plaque or nodule with deceptive borders
• Central dell often present
• Pain, burning or paresthesia
• The clinical “edge” of the lesion is very deceptive. At surgery the tumor invariably is much larger
• Mohs surgery is an excellent treatment option
• The image below shows a recurrent tumor

Histological features

• Poorly circumscribed
• ? sweat gland or sweat gland & follicular differentiation
• Rarely sebaceous differentiation (6 cases)
• Keratocysts with epidermoid keratinization
• Pilar keratinization is also sometimes present in the deeper reaches
• Clear cell change (if very marked, clear cell variant)
• Solid narrow epithelial strands (sometimes predominates and keratocysts absent (eccrine epithelioma, syringoid eccrine carcinoma)
• Minimal pleomorphism
• Mitoses very sparse or absent
• Ductal differentiation
• Invariable perineural infiltration*
• Dense fibrous stroma
• Solid variant
• High grade variant

Immunohistochemistry

• AE1/AE3 +ve
• CK15 -ve
• EMA & CEA show ductal differentiation
• BerEP4 –ve
• Low Ki67 expression
• Mutation in TP53 & loss of CDK2NA & CDKN2B (one case with metastases)

Prognosis

• Recurrences: 15-60%
• Recurrences may be greatly reduced with Mohs surgery
• MAC rarely involves nodes, exceptionally systemic spread (3)
• Radiotherapy is contra-indicated (if the tumor recurs, the dense fibrous stroma is worsened making surgery virtually impossible)
• Chemotherapy in systemic disease (carboplatin & paclitaxel)- one case

Differential diagnosis

• Desmoplastic trichoepithelioma*
• Trichoadenoma
• Squamoid eccrine ductal carcinoma
• Desmoplastic/sclerosing squamous cell carcinoma
• Morpheaform BCC
• Syringoma
• SCC with MAC-like differentiation

Desmoplastic trichoepithelioma

• Slowly growing white or yellow indurated plaque 3-8 mm in diameter
• Usually asymptomatic
• Face & neck ++, young adults
• 4F:1M
• May have a central dell
• High recurrence rate
• Confined to dermis*
• Comprises keratocysts and narrow epithelial strands typically showing a follicular connection
• Calcification often present
• No pleomorphism & mitoses generally absent
• No ductal differentiation (role of EMA and CEA)
• Perineural infiltration has recently been described (may account for the high recurrence rate*

Trichoadenoma

• Rare solitary 3-50 mm nodule on face and buttocks in adults
• Linear & verrucous variants
• Differentiated towards infundibulum (Images courtesy of Professor Jonhan Ho, KiKo)
• Cysts showing infundibular keratinization
• Calcification & foreign body giant cell reaction
• CK20 +ve Merkel cells

Squamoid eccrine ductal carcinoma

• Sun-damaged skin
• Elderly
• Face and neck++
• Males>Females
• Ulcerated
• nodule/plaque
• Often arises in an AK (Images courtey of Dr. Bipim Thingujam)
• Superficially shows features of squamous carcinoma with an epidermal origin
• Deep aspect- adenocarcinoma
• Pleomorphism often marked & mitoses generally numerous
• Recurrences-25% (series of 20 cases)
• Metastases 13% (1 with distant spread)