undifferentiated embryonal sarcoma of the liver (Monarch Disease Ontology identifier MONDO_0015795) can be described as follows. Embryonal sarcoma of the liver is a rare primary malignant hepatic neoplasm of childhood of mesenchymal origin. It can rarely occur in adults. It is characterized by abdominal mass, right upper quadrant or epigastric pain, nausea, anorexia, intermittent fever or headache. Also known as: UES, embryonal sarcoma of the liver, undifferentiated sarcoma of the liver.