A Rare Case of Trichilemmal Carcinoma of the Scalp.

Trichilemmal carcinoma (TC) is a rare, low-grade, malignant adnexal tumor. It is usually less than 3 cm long and arises from the external root sheath of the hair follicle, most commonly in sun-exposed areas of the body. The treatment of choice is wide local excision with tumor-free margins. We present an 88-year-old male patient who presented with an incidental large, dry, fumigating mass on his scalp for a one-year duration requiring surgical excision. The mass, initially thought to be a benign sebaceous cyst, was a 12-cm trichilemmal carcinoma diagnosed based on the histopathologic features of the mass. The specimen was composed of keratinaceous material and necrotic debris. The viable tumor was consistent with atypical squamous proliferation. The mass was fully excised down to the scalp on the first encounter, leaving no further tissue to excise. The patient's scalp site remained clean and without bleeding or recurrence. Currently, there is an increasing incidence of trichilemmal carcinoma. The pathophysiology of this disease is still unclear. The radiation from the sun is one of the factors that causes the growth of the lesions due to its location and distribution. Trichilemmal cysts can also transform into malignant trichilemmal carcinomas due to the p53 deletion. TC has a non-aggressive course despite its aggressive histology. The prognosis is generally good as it has low metastatic potential, like cutaneous squamous cell carcinoma. However, TC with metastasis has a poor prognosis, and there is no consensus yet on treatment. For non-metastatic TC, simple surgical excision with adequate (0.5-1 cm) margins is an effective treatment. Different studies use different margins, and there is no consensus on the measurement for margin excision. Regular follow-up is recommended, but further studies regarding follow-up schedules are needed. Furthermore, despite the common use of chemotherapy in cases of malignant TC, only a limited number of studies have explored this treatment approach. Given the increasing incidence of the disease, we highly recommend more research to address this knowledge gap.