Trichilemmal carcinoma
Tricholemmocarcinoma
Trichilemmal carcinoma is a rare malignant adnexal tumour showing differentiation toward the outer root sheath of the hair follicle. Despite an alarming histological appearance — with clear-cell atypia, mitoses and infiltrative growth — its clinical course is generally indolent, with low rates of recurrence and metastasis when widely excised. It typically presents on chronically sun-damaged skin of the head and neck of elderly patients. Distinction from squamous cell carcinoma is important, as treatment intensity and surveillance are less aggressive.
Clinical features
- Slowly enlarging, pink/red, occasionally ulcerated nodule, plaque or keratotic papule.
- Most common on the face, scalp, ears and dorsal hands of elderly Caucasians.
- Often present for months to years before diagnosis.
- Usually clinically indistinguishable from cSCC, BCC, AK or amelanotic melanoma.
Histology & differential
- Lobular proliferation of glycogen-rich, clear-cell keratinocytes with peripheral palisading and PAS-positive basement-membrane material — recapitulating the outer root sheath.
- Significant cytological atypia, mitoses and infiltrative deep border.
- Trichilemmal-type keratinisation (abrupt without keratohyaline granules).
- Differential:
- Trichilemmoma (benign) — well-circumscribed, no atypia; multiple lesions in Cowden syndrome / PTEN hamartoma tumour syndrome — multiple facial trichilemmomas are a major criterion for PHTS and warrant referral to clinical genetics.
- cSCC clear-cell variant — diffuse atypia, no peripheral palisading or PAS-positive basement membrane.
- BCC — basaloid, more uniform palisading; BerEP4-positive.
- Cutaneous metastasis from clear-cell renal cell carcinoma — PAX8, RCC marker positive.
Management
- Wide local excision with 5 mm clinical margins; Mohs micrographic surgery for facial sites.
- Sentinel lymph node biopsy not routinely indicated given indolent behaviour.
- Adjuvant radiotherapy reserved for incomplete margins, recurrent disease or rare nodal metastasis.
- Systemic therapy not standardised given rarity of metastasis.
Prognosis
Excellent — local recurrence 5–10% with conventional excision, much lower with Mohs. Regional or distant metastasis exceedingly rare. Standard skin cancer follow-up is appropriate.
References
- Reis JP et al. Trichilemmal carcinoma — review of 8 cases. J Cutan Pathol; 1993.
- Hamman MS et al. Trichilemmal carcinoma — clinical and pathological review. J Drugs Dermatol; 2018.
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