Slowly growing nodule in supralabial region

Apocrine mixed tumor of the skin.

Discussion

Mixed tumor of the skin (chondroid syringoma) is a rare tumor that was first described in 1859 by Billroth and is considered analogous to pleomorphic adenomas of salivary glands.^[1] This tumor typically presents in the middle-aged individuals and males are more commonly affected than females. It usually presents as a solitary, asymptomatic, flesh-colored or reddish, well-circumscribed and slow-growing benign tumor of the head and neck involving especially the nose, upper lip and cheek.^[2],[3] Malignant chondroid syringoma is rarer and occurs typically in women and appears on the extremities or trunk.^[2]

Chondroid syringoma contains both epithelial and mesenchymal elements. Most of them are classified as apocrine chondroid syringoma.^[3] It consists of a multilobulated and well-delimited tumor in the deep dermis or subcutaneous fat with an epithelial component distributed through a myxoid, chondroid and fibrous stroma.^[3],[4] The epithelial component is composed of clusters and solid cords of cells as well as tubuloalveolar and ductal structures. The tubuloalveolar structures are lined internally by two or more rows of pale-staining eosinophilic cytoplasm and oval basophilic nuclei cells (epithelial cells) and externally by pale-staining cytoplasm and hyperchromatic-spindled nuclei cells (myoepithelial cells). Tubuloalveolar structures intersect in a retiform fashion. Decapitation secretion is found in most cases. The ducts are lined by cuboidal epithelium. In some of these ducts, keratinous cysts may form. Apocrine chondroid syringoma can present a wide range of metaplastic changes and differentiation in the epithelial, myoepithelial and the stromal component.^[3],[4] In the epithelial component, apocrine, follicular and sebaceous differentiations are the most frequent.^[3] Lipomatous metaplasia, chondroid metaplasia and osseous metaplasia are occasionally present.^[3] Some of these tumors are classified as atypical mixed tumor due to their borderline features of malignancy with an infiltrative pattern but without dissemination in their follow-up.^[1],[3] Immunohistochemically, the epithelial component expresses low molecular weight keratin, epithelial membrane antigen and carcinoembryonic antigen.^[5] The myoepithelial cells express vimentin, S-100 and sometimes muscle-specific actin. Finally, stromal cells are vimentin and S-100 positive.^{[1],[2],[4],[5]}

The main differential diagnosis should include mixed tumor of salivary gland (for tumors located in the facial region), pilomatricoma, chondroma, osteoma, mesenchymal hamartomas of the skin, dermoid or epidermoid cysts, neurofibromas, dermatofibromas and basal cell carcinomas.^[2],[5] Definitive diagnosis can be made by total excision and histopathologic examination.^[2] The combination of epithelial and mesenchymal components is the key finding that allows the correct differentiation from other skin tumors.^[4]

The treatment of choice is complete excision, although electrodesiccation, dermabrasion and vaporization with argon or CO₂ laser could be other options.^[1],[2],[5] Mohs surgery has been used in one patient with recurrent benign chondroid syringoma of the eyebrow with no recurrences.^[5]

We highlight the importance of clinical suspicion of this entity when we face a slowly growing nodule. Histological examination will be essential for the correct diagnosis, and complete excision will be necessary for avoiding recurrences.