DP19: A masquerade ball of cells

Jasmine Mann,¹ Zahra Moledina,² David Veitch,³ Karim Eldib,² Somaia Elsheik² and Sandeep Varma²

¹University Hospitals of Derby and Burton NHS Foundation Trust, Derby, UK; ²Nottingham University Hospitals NHS Trust, Nottingham, UK; and ³University Hospitals of Leicester NHS Trust, Leicester, UK

An 82-year-old woman presented with a 4-year history of an asymptomatic, slow-growing lesion on the right medial cheek. On examination there was a 6 × 7 mm smooth shiny lesion with a rolled border and telangiectasia under dermoscopy, consistent with a clinical diagnosis of basal cell carcinoma (BCC). In view of the suspicion of a BCC and location, which would likely need Mohs micrographic surgery, a 3-mm diagnostic punch biopsy was arranged. Histology showed skin containing part of an epithelial, infiltrative dermal tumour. The epidermis displayed focal dysplastic changes but no carcinoma in situ. The tumour consisted of small nests and strands of cells with a single prominent nucleolus and low mitotic activity. There was focal apoptosis, and suggestion of squamous differentiation. A prominent feature was the presence of ductal differentiation, highlighted by carcinoembryonic antigen (CEA) and epithelial membrane antigen (EMA). There was no lymphovascular or perineural invasion and the background stroma appeared slightly sclerotic. The diagnosis was therefore made of a squamoid eccrine ductal carcinoma (SEDC). SEDC is a rare sweat gland carcinoma with squamous and ductal differentiation and accounts for < 0·01% of cutaneous malignancies (Kim YJ, Kim AR, Yu DS. Mohs micrographic surgery for squamoid eccrine ductal carcinoma. Dermatol Surg 2005; 31: 1462–4). Tumours present as nodules or plaques with a predilection for the head and neck (van der Horst MP, Garcia-Herrera A, Markiewicz D et al. Squamoid eccrine ductal carcinoma. Am J Surg Pathol 2016; 40: 755–60). This histological diagnosis can be challenging owing to its morphological similarity to other eccrine neoplasms, in particular microcystic adnexal carcinoma. Classically, it has a biphasic appearance with an infiltrative and poorly defined growth pattern, extending deep to the dermis with prominent squamous differentiation. Immunohistochemistry for ductal differentiation is usually positive for CEA and EMA. Differential diagnosis includes squamous cell carcinoma, microcystic adnexal carcinoma and porocarcinoma with squamous differentiation. It is thought to have low-grade malignant potential with aggressive local behaviour, but there is limited literature on prognosis and follow-up. There are no standard recommended clinical margins, but the preferred treatment of choice is Mohs micrographic surgery for complete excision with clear margins. Local recurrence of eccrine carcinomas has been reported to be higher following conventional surgical excision (10–70%) than following Mohs micrographic surgery (0–5%), at an average of 30·9 months follow-up. Our patient proceeded to have Mohs micrographic surgery, with two stages required for tumour clearance. The debulk and two stages were double-read with a histopathologist. The defect was repaired with a rhombic transposition flap with no evidence of recurrence or metastasis at the 12-month follow-up. She continues to be followed-up every 3 months.