An aggressive malignant mesenchymal neoplasm of the nervous system or soft tissues. It is characterized by the presence of a sarcomatous component (most often rhabdomyosarcoma) and a ganglionic or a neuroectodermal component. The disease is ectomesenchymoma (MONDO_0002855, a Monarch Disease Ontology entry). Also known as: malignant ectomesenchymoma, rhabdomyosarcoma with ganglionic differentiation, rhabdomyosarcoma with ganglionic differentiation (morphologic abnormality), sarcoma with ganglionic or neuroectodermal differentiation.