Merkel cell tumour with leiomyosarcomatous differentiation

Aims: To report and confirm the identity of tumour cells showing leiomyosar comatous differentiation in a regional lymph node containing metastatic Mer kel cell tumour. Methods and results: A 79-year-old woman was found to have metastatic Merke l 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 ident ical to that of the primary tumour but there was an additional focus of loo se spindle cells. Immunocytochemical staining showed the coexpression of cy tokeratin 20, neurofilament and desmin in these sarcomatous cells. Conclusion: This, to the best of our knowledge, is the first report of Merk el cell carcinoma showing sarcomatous differentiation, and adds to the expa nding morphological spectrum of malignant biphasic tumours.