Microcystic adnexal carcinoma induced by multiple radiation therapy

We present an 84‐year‐old Caucasian man (Fitzpatrick classification: skin type II) with microcystic adnexal carcinoma (MAC) on his left cheek and a 15‐year history of recurrent squamous cell carcinoma (SCC) of the head, treated with numerous surgical interventions and multiple palliative 60‐Gy radiation therapy. In 1996, the patient developed a nontender, indurated, irregularly marked, erythematous lesion on his left cheek (1.5 × 1 cm). Furthermore, the patient suffered from radiodermatitis due to previous radiotherapy ( Fig. 1 ). Punch biopsy and a subsequent wedge excision showed features of both SCC and eccrine carcinoma. Histopathologic and immunohistochemical tests of the tumor revealed a diagnosis of MAC. The patient underwent Mohs' micrographically controlled surgery to obtain tumor‐free peripheral soft tissue margins. There was no evidence of any lymphatic invasion or distant metastasis in the physical and laboratory examination. So far, the patient has not developed any recurrences. Clinical picture of MAC showing features of radiodermatitis image Following excision, the biopsy specimen (4 × 2.6 × 1 cm) was fixed in Dubosq‐Brazil and routinely processed for staining with hematoxylin and eosin. The neoplasm extended into the subcutaneous tissue with rare connection to the overlying epidermis ( Fig. 2 ). Follicular cysts with amorphous eosinophilic keratin and comma‐like tails of aggregates of epithelial cells were a prominent feature ( Fig. 3 ). Perineural invasion was evident, but there were only a very few mitotic figures. Immunohistochemistry on paraffin‐embedded tissue blocks was performed, showing strong labeling on dilated ducts for carcinoembryonic antigen (CEA), epithelial membrane antigen (EMA) in the lumina of tumor cells, and positive staining for anticytokeratin KL1 (55–57 kDa) and S‐100 protein. The latter was negative in ductal structures, but stained dendritic cells. Panoramic view of the tumor demonstrating poorly circumscribed and deeply infiltrative growth patterns. Rare connection of the tumor with epidermal structures is evident (hematoxylin and eosin, × 40) image Comma‐like tails of aggregates of epithelial cells and follicular cysts with amorphous eosinophilic keratin (hematoxylin and eosin, × 150)