Trichoblastoma

Epidemiology and Etiology:

Common sites:

Gross features:

Histologic features:

• nests, sheets, or trabeculae of germinative basaloid cells
• hair bulb differentiation at the edge of the nests
• keratin cysts (small) usually (not seen in BCC)
• follicular papillae usually (not seen in BCC)
• mild to moderate fibrosis surrounding
• prominent demarcation from normal dermis
• stromal-stromal separation
• peripheral palisading present
• brisk mitotic rate
• no stromal clefting typically
• no mucin production (except rarely)
• low apoptotic rate

Immunophenotype:

Marker:	Sensitivity:	Specificity:
CD34 (stroma) (neg in BCC)
CK7/8 (neg) (focal in BCC)

Molecular features:

Other features:

• very rarely trichoblastic carcinoma may arise from trichoblastoma

References:

• Barnhill 2004
• Essentials of AP 2006