Proliferating Trichilemmal Cyst / Tumour
Proliferating Pilar
Tumour
Epidemiology and Etiology:
- Middle age or elderly women particularly
- Repeated episodes of rupture and
re-epithelialization of trichilemmal (pilar) cyst, likely
Common sites:
Gross features:
- Solitary usually
- Subcutaneous nodule or lobulated mass
- May ulcerate or “marsupialize”
- Massive cutaneous horns have been reported
- Malignant proliferating trichilemmal
(pilar) tumour) is 4
cm on average
Histologic features:
- Lobules of squamous epithelium of varying sizes
- Peripheral palisading in some
- Distinct surrounding basement membrane material
- Amorphous eosinophilic keratin without a
granular layer (trichilemmal keratinization)
- Intermized infundibular type keratinization maybe
- Apocrine or sebaceous differentiation maybe
- Squamous eddy formation maybe
- Calcification maybe
- Clear cell change maybe (outer root sheath
epithelium differentiation
- Nuclear pleomorphism
maybe (limited cytologic atypia)
- Mitotic rate up to 1/HPF
- Stromal infiltration, small foci (maybe) (such
lesions otherwise show a benign biologic behavior)
- Malignant proliferating trichilemmal
(pilar) tumour:
- Areas with little pilar
differentiation, squamoid or basaloid
- Conspicuous nuclear atyipa
- High mitotic activity (4-5/HPF)
- Dyskeratotic cells
- Necrosis
- Stromal invasion
Immunophenotype:
Marker:
|
Sensitivity:
|
Specificity:
|
|
|
|
Molecular features:
Other features:
- Benign, but there exists a malignant
proliferating trichilemmal (pilar)
tumour as well, which may show lymphatic spread
- Recurrences have been reported – complete excision
is indicated
References: