Trichoblastic Carcinoma Arising from a Nevus Sebaceous.

Nevus sebaceous is a hamartoma of the cutaneous structures that often presents at birth and typically involves the face and scalp. Nevus sebaceous is frequently complicated by the development of a variety of other benign or malignant neoplasms. The most frequently reported benign neoplasms are trichoblastoma and syringocystadenoma papilliferum. Malignant tumors are much less frequently observed in association with nevus sebaceous and include basal cell carcinoma, squamous cell carcinoma, sebaceous carcinoma, and others [1]. However, no previous reports have described trichoblastic carcinoma occurring secondarily to nevus sebaceous. We report a case of malignant trichoblastoma that arose from nevus sebaceous of the scalp in a 38-year-old woman. A 38-year-old woman visited our clinic with a mass arising from a birthmark on the left parietal scalp. Six months prior to the visit, an erythematous mass had enlarged gradually in the plaque. Her chief complaints associated with the mass were itching, pain, and bleeding easily after small traumas. Physical examination of the scalp revealed a 5 × 2-cm yellowish, verrucous, hairless plaque, and a distinct 1.5 × 1.5-cm erythematous nodule was contained within it (Fig. 1). She had no personal or family history of underlying skin diseases or malignancies. A punch biopsy was done from the erythematous nodule, and showed that the mass was a malignant skin adnexal tumor. Therefore, she underwent complete surgical excision with 0.5 mm of normal skin surrounding the margins of the nevus sebaceous (Fig. 2). A frozen section biopsy showed that no tumor cells were present in the resection margin. The skin defect was then covered with a transpositional flap and primary closure was performed (Fig. 3). A histopathologic examination of the mass was performed, revealing the presence of a nodular tumor, which was diagnosed as trichoblastic carcinoma. It was composed of basaloid epithelial nests and strands. Some nodules showed central necrosis (Fig. 4). Nuclear atypia was present, as well as increased mitotic activity in a high-power view (Fig. 5). After confirming its malignancy, the patient was carefully evaluated for evidence of metastasis. A full body positron emission tomography-computed tomography (PET-CT) scan revealed no regional or distant metastasis. The patient is now under followup care. Malignant trichoblastoma is a rare malignant adnexal tumor originating from the hair germ cells. Malignant changes in trichoblastoma may be related to its epithelial component (trichoblastic carcinoma), stromal component (trichoblastic sarcoma), or both (trichoblastic carcinosarcoma). Trichoblastic carcinoma usually presents on the scalp and face in