A slowly growing, highly vascularized papule in a 4-year-old girl

A 4-year-old Caucasian girl was referred to our Paediatric Dermatology Unit for evaluation of a dome-shaped papular lesion on the columella. The papule had appeared 8 months earlier and had been reported as progressively growing, but was completely asymptomatic. On examination, the lesion was 4 mm in diameter and was elastic hard on palpation (Figure 1a). Noncontact polarised dermoscopy showed a highly vascularises pattern, with out-of-focus arboriform telangiectasias on a pinkish background. There was no pigment network or other dermoscopic signs suggestive of a melanocytic lesion (Figure 1b). Given the nonspecificity of the clinical and dermoscopic findings and the progressive enlargement over time, the lesion was surgically removed and histological examination was carried out (Figure 2). Cutaneous myoepithelioma. Histopathology showed a well-circumscribed neoplasm centred within the dermis with lobulated architecture (Figure 2a), characterised by a proliferation of ovoid and spindle histiocytoid cells with pale eosinophilic cytoplasm, organised in cords and nests within a myxoid matrix (Figure 2b). Tumour cells were characterised by no significant nuclear pleomorphism, inconspicuous nucleoli, and no mitoses; no glandular or ductal differentiation was evident. Tumour cells express several neuroid markers (S-100 protein [Figure 3a], glial fibrillary acidic protein, and SRY-related HMG-box 10 [SOX10] protein), one epithelial marker (epithelial membrane antigen [EMA]) (Figure 3b), and focal expression of smooth muscle actin. The coexpression of neuroid and epithelial immunohistochemical markers, in association with the absence of any glandular or ductal differentiation, led to the histopathological diagnosis of cutaneous syncytial myoepithelioma. The absence of cytologic atypia made it possible to exclude malignancy. Cutaneous myoepithelioma is a rare neoplasm composed primarily of myoepithelial cells, and represents one end of a spectrum of myoepithelial neoplasms of the skin and soft tissue also including mixed tumours/chondroid syringomas and myoepithelial carcinomas. These tumours display a wide histopathological spectrum and immunophenotypical profile.1, 2 Mixed tumours/chondroid syringomas typically show tubuloductal differentiation, which is also present in salivary gland pleomorphic adenoma (benign mixed tumours of salivary glands). Cutaneous myoepithelioma, instead, lacks any ductal differentiation and is predominantly composed of spindled or ovoid myoepithelial cells. While in salivary gland myoepithilal neoplasms malignancy is defined by architectural features, in their skin counterpart cytologic atypia is currently the only known predictor of an aggressive behaviour.2, 3 Only 20% of soft tissue and skin myoepithelial neoplasms occur in children, but they are malignant in up to 65% of cases. They usually present as subcutaneous nodules on the extremities and proximal limb girdles, and affect males and females equally.1, 2, 4 From a genetic point of view, EWSR1 gene rearrangement is found in up to 45% of myoepithelial tumours of skin and soft tissue, thus supporting the idea of a spectrum of neoplasms. Several fusion partners have been detected so far; however, the significance, if any, of the gene fusion products is not well understood.2, 5 Differential diagnoses of myoepithelial neoplasms include epithelioid fibrous histiocytoma, early juvenile xanthogranuloma, Spitz naevus, ossifying fibromyxoid tumour and epithelioid sarcoma.6 In particular, from a dermoscopic point of view, a highly vascularises papular lesion with no pigment network in a child should raise suspicion for a spitzoid neoplasm.7 To the best of our knowledge, dermoscopic features of cutaneous myoepithelioma have not been described. Further studies on this may provide an additional tool for the differential diagnosis of these uncommon tumours. Although cutaneous myoepithelioma is characterised by a benign behaviour, there is risk of local recurrence (up to 20%), especially in case of incomplete resection; therefore, regular follow-up after surgical removal is highly recommended.8 In our case, follow-up visits were scheduled every 6 months for 2 years, and no signs of local recurrence were observed. All authors contributed to designing and conducting the work, draughting and revising the manuscript and approved the final version for submission. The authors declare no conflict of interest. The parents/guardians of the minor patient included in this manuscript have provided written informed consent for the child's participation in the study, as well as for the use of the child's deidentified, anonymized, aggregated data, and case details (including photographs) for publication. The data that support the findings of this study are available from the corresponding author upon reasonable request.