Collision Tumor in the Lower Eyelid: Basal Cell Carcinoma Adjacent to Trichoepithelioma.

Abstract

The coexistence of 2 neoplasms in a single cutaneous specimen is unusual. We describe a lower eyelid lesion in which the biopsy revealed a trichoepithelioma (TE) and an adjacent basal cell carcinoma (BCC). A 57-year-old female patient reported a 5-year history of lower eyelid pruritus and had been treated for blepharitis elsewhere. She was referred for eyelid evaluation due to the presence of a plaque, loss of eyelashes, and areas of inflammation in the right lower eyelid. She underwent tumor excision, and the eyelid was reconstructed using an orbicularis muscle advancement flap combined with a free tarsoconjunctival graft and a skin graft. Preoperative photographs show an extensive lesion, with madarosis in the right lower eyelid (Fig. A and B). Biopsy specimen from the right lower eyelid revealed 2 different tumor types: a TE and an adjacent BCC (Fig. C and D). A focus of TE is seen (left) juxtaposed with a focus of BCC (right). The area containing the TE was composed of basaloid cell nests and horn cysts, embedded within an organized stroma. Areas of cicatricial fibrosis and foreign body-type reaction were also observed. These histopathology features were consistent with that of a desmoplastic TE (DTE). The adjacent BCC area showed proliferation of atypical basaloid cells with peripheral palisading. Cytoplasm was basophilic and relatively scant, nuclei were large and mildly irregular, and contained grumous chromatin and mitotic figures. Trichoepithelioma is a benign tumor of follicular origin with 3 distinctive variants: multiple familial, solitary, and DTE. DTE is a rare benign adnexal tumor, derived from basal cells in the outer root sheath of the hair follicle, histologically characterized by narrow strands of basaloid tumor cells, keratinous cysts, and a desmoplastic stroma. TEs and BCCs both present with nests of basaloid cells. Histologic features that favor TE include the following: architectural symmetry, horn cysts, and associated giant cell reaction (rare in BCC), papillary mesenchymal bodies, no high-grade atypia, no or very low mitotic activity, monomorphic nuclei, no tumor necrosis, no peripheral clefting. The presence of peripheral palisading of basaloid cells, clefting between the epithelial and stromal components, necrosis, and high mitotic activity are associated with BCC. When histologic examination does not permit to differentiate a TE from a BCC, immunohistochemical stains, such as BCL2, CD10, CD34, AR, may be useful. Transformation of TE to BCC is rare and usually occurs in the setting of multiple TEs. A possible way to investigate transformation would be to compare the DNA of both tumors to find a common mutation. In our patient, it is more likely that this is a collision tumor (coexistence of 2 different tumors in the same lesion). Concomitant presence of a TE and a BCC is rare, and, to the best of our knowledge, this is the only case showing a DTE adjacent to a BCC, involving the eyelid. This case highlights that benign and malignant pathology can coexist within the same lesion. Special attention should be addressed to collision tumors since, in these cases, a small incisional biopsy might not be sufficient for accurate diagnosis.Fig.: Basal cell carcinoma adjacent to trichoepithelioma. A and B, A 57-year-old female patient presented an extensive lesion, with madarosis in the right lower eyelid. C and D, Hematoxylin and eosin stain of the biopsy specimen (100× and 200×) revealed 2 different tumor types: a focus of trichoepithelioma is seen (left) juxtaposed with a focus of basal cell carcinoma (right).