A usually malignant neoplasm composed of primitive (immature) tissues that resemble fetal tissues. Medulloblastoma, Ependymoblastoma, Pineoblastoma, and Wilms tumor are representative embryonal neoplasms. --2003. The disease is Monarch Disease Ontology entry MONDO_0005564 (embryonal neoplasm). Also known as: embryo neoplasm, embryonal tumor, embryonal tumour.