DP08: Metastatic cutaneous myoepithelial carcinoma: a case report

Sarah McCusker,¹ Alastair Milne,¹ Steven Lo² and Amrita Randhawa¹

¹Queen Elizabeth University Hospital and ²Glasgow Royal Infirmary, NHS Greater Glasgow and Clyde, Glasgow, UK

Myoepithelial carcinoma (MEC) are uncommon tumours, typically occurring in the salivary glands (Ellis GL, Auclair P. Tumors of Salivary Glands, Atlas of Tumor Pathology. Washington, DC: Armed Forces Institute of Pathology, 1996). Cutaneous MECs are extremely rare. Herein, we present a case of cutaneous MEC with metastatic spread. An 84-year-old man was referred to dermatology in February 2020 with a 2-month history of an asymptomatic lump to the vertex scalp. There had been no increase in size. He had a recent diagnosis of rectal adenocarcinoma, with no evidence of metastatic disease on computed tomography, managed with palliative radiotherapy. Past medial history included diabetes mellitus, abdominal aortic aneurysm, transient ischaemic attacks, angina and aortic stenosis. Initial examination revealed a 22 × 18 mm fixed nodule to the vertex scalp. There was no associated lymphadenopathy. A diagnostic biopsy was arranged. This demonstrated a malignant tumour displaying S100 and focal epithelial marker immunopositivity for AE1/3, MNF, cytokeratin 5 and P63. A few cells showed positive staining with glial fibrillary acidic protein and smooth muscle actin. The previous colorectal cancer was reviewed and was of a different morphology. A diagnosis of MEC was made. His case was discussed at the national sarcoma multidisciplinary team meeting. Further investigations were arranged, and surgical excision was considered. Unfortunately, on review in clinic in June 2020 there was evidence of six firm subcutaneous lumps surrounding the primary lesion, and one to the left temporal scalp, consistent with cutaneous metastases. There was a palpable lymph node in the right cervical chain. Computed tomography of the head, neck, thorax, abdomen and pelvis demonstrated multiple cranial scalp lesions, multisite bilateral neck lymphadenopathy and a left lower lobe pulmonary metastasis, which was felt to be secondary to his rectal cancer. Magnetic resonance imaging of the scalp demonstrated multifocal scalp lesions, with one infiltrating the skull but not breaching the inner table. Multidisciplinary review indicated that surgery was not appropriate, and he was referred for consideration of palliative radiotherapy. Following discussion with the patient it was decided that the best route was for supportive care. He died 11 months after the initial diagnosis. Cutaneous MEC is exceedingly rare and has a high rate of recurrence (~30%) and metastases (~15%) (Rastrelli M, Passuello N, Cecchin D et al. Metastatic malignant soft tissue myoepithelioma: a case report showing complete response after locoregional and systemic therapy. J Surg Case Rep 2013; 3: rjt109). MEC consists of myoepithelial cells, which display features of smooth muscle and epithelial cells (Rastrelli et al.). They commonly present as painless, slow-growing nodules. Treatment of choice is surgical excision. Isolated limb infusion has been used in those occurring on the extremities and radiotherapy is another option. This case serves to highlight the importance of recognizing this rare cutaneous malignancy, and its high potential for metastatic disease.