AGGRESSIVE TRICHOEPITHELIOMA VERSUS KERATOTIC BASAL CELL CARCINOMA

A 43‐year‐old white man presented with an infiltrative le‐sion on the left nasolabial fold, which had grown slowly over 15 years. There was a history of moderate sun expo‐sure. Prior history was negative for cutaneous carcinomas. Family history was negative for trichoepithelioma. Physical examination revealed a patient with a fair complexion, blue eyes, light skin, and light brown hair. There was evidence of severe actinic damage manifested by marked solar elas‐tosis of the face. A 1.5 × 1.3 cm infiltrative, depressed, skin‐colored plaque, with elevated pearly borders was noted on the left nasolabial fold. There was nodule formation with superficial ulceration in the center of the lesion (Fig. 1). No other skin tumors were present. A punch biopsy showed a deeply infiltrating tumor. Sub‐sequently, the tumor was excised by Mohs micrographic surgery in six stages, revealing deep and wide clinically un‐detected invasion into the orbicularis oris, zygomaticus minor, and the levator labii superioris muscles. The final size of the defect was 5.0 × 5.0 cm (Fig. 2). Reconstruction was later performed by otolaryngology with satisfactory results. Pathological Study: The tumor was composed of multiple islands of basaloid cells embedded in a dense fibrotic stro‐ma. Some islands showed peripheral palisading of their cells (Fig. 3). Other areas contain numerous horn cysts with abrupt and complete keratinization surrounded by basaloid cells (Fig. 4). Areas of calcification and foreign body reac‐tion are present secondary to ruptured cysts. Stromal‐stro‐mal clefting characteristic of trichoepithelioma is seen adjacent to some tumor islands (Fig. 5). The tumor infil‐trates into the underlying muscle (Fig. 6). Stromal muco‐polysaccharide deposition and stromal‐tumor separation as seen in basal cell carcinoma (BCC) were not present.