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Case Reports

Abstract

Trichilemmal carcinoma (TC) is an extremely rare, low-grade malignant tumor arising from the external root sheath of the hair follicle, with excellent prognosis. It is most often associated with ultraviolet radiation exposure and occurs on the head and neck region of elderly individuals. Median age at diagnosis is 73 years, with only a few reported cases in patients under 40. TP53 mutations have been reported in a few cases.

Herein, we report a case in a 26-year-old female with history of atopic dermatitis since childhood and pilar cyst who presented with an enlarging, non-tender nodule on the right parietal scalp. Examination revealed a 3.1 cm erythematous nodule with focal crusting. An excisional biopsy demonstrated a focally infiltrative, multicystic dermal-based tumor with nodules and islands of squamoid to clear cells and keratinous debris. The tumor lobules demonstrated peripheral palisading, thickened basement membrane and abrupt keratinization lacking a granular layer in the center, consistent with trichilemmal keratinization. The tumor nodules were present in a desmoplastic stroma and there was focal giant cell reaction indicating rupture. Abundant mitotic figures and focal area of infiltration was present. Immunohistochemical studies demonstrated that the tumor cells were diffusely positive for p53 and negative for androgen receptor and Ep-CAM. The differential diagnosis included proliferating pilar (trichilemmal) tumor, clear cell squamous cell carcinoma, clear cell basal cell carcinoma and TC. Overall, findings were consistent with TC. The tumor was completely excised by Mohs surgery. The patient is doing well on 43 months follow up with no recurrence.