Thirteen cases of a unique cutaneous tumor are presented. The lesions presented as single, nondescript, skin-color nodules. Eleven were located on the head and two were on the legs. The male/female ratio was 8:5. The age at diagnosis ranged between 21 and 55 years (mean: 39). The duration of the lesions was from several months to more than 20 years. All tumors were excised and did not recur. The tumors typically presented as well-circumscribed nodules with scant or no epidermal connections. (One example, however, had a plate-like configuration amply connected with the basal layers of the epidermis.) The proliferation consisted of multiple, rounded lobules of basaloid cells with some degree of peripheral palisading, immersed in a dense, fibrous stroma. There was an intense infiltrate of small lymphocytes within the lobules, with some spillage into the stroma. No clear adnexal differentiation was noted except for rare isolated cells showing apparent sebaceous differentiation within the tumor lobules. Areas of central keratinization were also present. Numerous cells with ample amphophilic cytoplasm, large vesicular nuclei, and prominent nucleoli were also seen. Immunohistochemistry confirmed the presence of keratin within tumor cells. Common leukocytic antigen highlighted the intense intra-lobular lymphocytic component. Vimentin not only highlighted the stromal fibroblastic component, but also stained scattered intralobular cells. Epithelial membrane antigen was positive within some of the large intraepithelial cells. S-100 protein was extensively positive within dendritic intralobular and stromal cells. Lymphocytic markers demonstrated a polyclonal B and T population. This unique tumor appears to represent a form of adnexal neoplasm with basaloid features, possibly immature pilosebaceous differentiation.
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