[Infantile rhabdomyofibrosarcoma. An aggressive tumor in the spectrum of spindle cell tumors in childhood].

We report a case of an intrathoracic, extrapleural, infantile rhabdomyofibrosarcoma in a 4-year-old boy. Histologically, the primary lesion showed extensive hyalinization and stroma sclerosis and was composed of relatively uniform spindle-shaped, at least focally rather polygonal tumour cells with scattered intracytoplasmatic globoid inclusions. Although chemo- and radiotherapy was given postoperatively, local recurrences and metastases in the lung and thymus have developed; the patient died of tumour disease 3 years later. Recurrences and metastases showed features of tumour progression with higher cellularity and increased mitotic activity. Immunohistochemically, the tumour cells stained strongly positive for vimentin, desmin, and muscle-specific actin, and at least focally for MyoD1; the tumour did not stain for alpha-smooth muscle actin, neural and epithelial markers, or CD34 and CD31. The differential diagnosis of these aggressive tumours in the spectrum of spindle-cell lesions in early childhood is discussed.