[Pelvic malignant ectomesenchymoma: a case report].

We report the case of a 19 month old boy referred to our institution because of a pelvic tumor initially identified as an embryonal rhabdomyosarcoma and treated with surgery and chemotherapy. Eight years after the initial surgery, a local tumor recurrence with bone metastasis was found. Histological examination and immunohistochemistry showed a double differentiation with both muscular and neuronal cells. This double differentiation was retrospectively found in the initial tumor, then allowing the diagnosis of malignant ectomesenchymoma also called gangliorhabdomyosarcoma. This rare tumor, occurring mainly during childhood, is composed of neuroblasts and / or ganglion cells and of malignant mesenchymal cells (usually rhabdomyosarcomatous cells).