Undifferentiated (embryonal) liver sarcoma of childhood: evidence of leiomyoblastic differentiation.

This report describes the clinical, histopathologic, and ultrastructural features of a tumor of the liver arising in an 11-month-old infant and displaying the morphology of undifferentiated (embryonal) sarcoma. The gross presentation and clinical manifestations showed some overlap with features often considered distinctive of embryonal rhabdomyosarcoma primary of bile ducts. However, electron microscopic study disclosed only fibroblastic and leiomyoblastic differentiation in biopsies of recurrent tumor, close to 2 years after the original diagnosis. Theoretical implications of this finding are discussed.