An aggressive malignant mesenchymal neoplasm that arises from the liver and usually occurs in older children. It is composed of immature spindle, stellate, polymorphous, and giant cells. The disease is undifferentiated (embryonal) sarcoma (MONDO_0005102). Also known as: UES, embryonal sarcoma, embryonal sarcoma (undifferentiated sarcoma), embryonal sarcoma, undifferentiated, sarcoma, undifferentiated, malignant, undifferentiated sarcoma.