BOTRYOID-TYPE EMBRYONAL RHABDOMYOSARCOMA OF LIVER IN A YOUNG CAT

An unusual malignant mesenchymal tumor arising in the liver of a 2-yea r-old cat is described. Histologically, the tumor showed considerable variation in growth pattern, cellularity, and cell types. Phenotypical diversity was confirmed by immunohistochemistry, showing expression o f desmin, vimentin, S-100, and neuron-specific enolase in various area s of the tumor On the basis of histopathology, immunohistochemistry, e lectron microscopy, and gross morphology, the tumor was classified as botryoid-type embryonal rhabdomyosarcoma. Differential diagnosis inclu ded so-called undifferentiated (embryonal) sarcoma of the liver, a rar e tumor of the pediatric age group in humans. Problems of tumor hetero geneity and differentiation in mesenchymal tumors are discussed.