A trichogenic tumor with aggressive features initially diagnosed as basal cell carcinoma

Trichoblastic carcinoma is a rare carcinoma often arising in a pre-existing trichoblastoma. It may resemble basal cell carcinoma, posing a diagnostic challenge. Trichoblastic carcinoma is divided into low-grade and high-grade tumors. Low-grade tumors resemble basal cell carcinomas and are therefore synonymous in some classifications. High-grade tumors, which commonly present on the scalp in older individuals or in patients with Brooke-Spiegler syndrome, have been associated with a higher potential for distant metastasis and death. We present a case in which a 73-year-old female had a long-standing scalp nodule for over 30 years that rapidly increased in size. The patient's lesion was initially diagnosed as basal cell carcinoma on shave biopsy, but upon excision, revealed features concerning for trichoblastic carcinoma such as brisk mitotic activity and comedo-like necrosis. Sudden change in an atypical scalp lesion that has been present for many years should increase suspicion for an atypical trichogenic tumor, such as trichoblastic carcinoma.