Primary cutaneous sarcomas showing rhabdomyoblastic differentiation.

Rhabdomyosarcoma is a rare soft tissue neoplasm most commonly encountered in childhood and adolescence which has a predilection for the head and neck area, the genito-urinary tract and the extremities. Primary cutaneous presentation is extremely unusual and has been rarely reported in the literature. Herein, we describe two cases of rhabdomyosarcoma arising in the dermis of a 9-year-old girl and an 86-year-old man. Clinically, the tumours presented as solitary plaque-like or nodular lesions confined to the skin of the nose and chest wall, respectively. Histologically, the tumour in the first patient corresponded to an embryonal rhabdomyosarcoma. The tumour recurred locally four times, and in the last recurrence, showed features resembling those of malignant 'triton' tumour with fascicles of S-100 protein-positive spindle cells admixed with the rhabdomyoblastic components. The tumour in the second patient corresponded to the solid variant of alveolar rhabdomyosarcoma. Immunohistochemical studies in both tumours showed positive labelling for muscle-specific actin, desmin and vimentin. Ultrastructural examination in one case showed clusters of intermediate filaments in the cytoplasm recapitulating abortive sarcomeric structures consistent with rhabdomyoblastic differentiation. Both patients developed repeated recurrences over a period of 2-4 years despite adequate surgical excision, and the second patient had an axillary lymph node metastasis. Primary cutaneous rhabdomyosarcoma should be considered in the evaluation of small 'blue cell' tumours or undifferentiated malignant neoplasms of the skin, and appropriate immunohistochemical studies in conjunction with electron microscopy should be employed for proper evaluation of such lesions.