Merkel cell tumour with leiomyosarcomatous differentiation

Aims: To report and confirm the identity of tumour cells showing leiomyosarcomatous differentiation in a regional lymph node containing metastatic Merkel cell tumour. Methods and results: A 79-year-old woman was found to have metastatic Merkel cell tumour within an axillary lymph node 4 months after excision of the primary tumour from the forearm. The lymph node was effaced by tumour identical to that of the primary tumour but there was an additional focus of loose spindle cells. Immunocytochemical staining showed the coexpression of cytokeratin 20, neurofilament and desmin in these sarcomatous cells. Conclusion: This, to the best of our knowledge, is the first report of Merkel cell carcinoma showing sarcomatous differentiation, and adds to the expanding morphological spectrum of malignant biphasic tumours.