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Case Reports

Abstract

A 73-year-old male presented with a tender scalp mass. The patient first noticed the mass 6 months ago and reported episodic bleeding from it. His previous cancer screening studies were unremarkable. Physical examination revealed a 4-cm flesh-colored, fungating, round nodule with an overlying ulcer on the right vertex. Shave biopsy of the mass showed invasive squamous cell carcinoma (SCC). Metastatic workup is equivocal. However, complete excision of the lesion revealed a proliferation of tumoral lobules with pushing margins in the dermis. The lobules are composed of atypical squamoid cells with clear cytoplasm, prominent nucleoli and frequent mitoses with foci of trichilemmal keratinization. At the periphery of the lobules, cellular palisading is evident with a surrounding eosinophilic vitreous basement membrane. Notably, a trichilemmoma is found adjacent to the lobules. A diagnosis of trichilemmal carcinoma (TC) was rendered. TC is a rare adnexal malignant neoplasm arising from sun-exposed and hair-bearing areas of the body. A biopsy does not always adequately demonstrate the architecture of the entire tumor, hence, a common pitfall is mistaking it for invasive SCC, its close and highly prevalent clinical and histologic mimic. It is imperative for pathologists to have a healthy threshold of speculation for this entity, since stage-dependent treatment differences from invasive SCC exist.