A FIBROSARCOMA IN THE SKELETAL-MUSCLE OF A CAPYBARA (HYDROCHOERUS-HYDROCHAERIS)

An 8-yr-old male capybara (Hydrochoerus hydrochaeris), a resident of a n urban zoological collection in upstate New York (USA), had a mass po steroventral to its left stifle; it was of unknown duration. The mass was a fibrosarcoma based on invasive sheets of interwoven spindle-shap ed neoplastic cells with moderate associated extracellular matrix comp osed of collagen fibers. Supportive immunohistochemical staining was p ositive f or vimentin but negative for cytokeratins, desmin, and myogl obin. The animal subsequently died of unknown causes. This is the firs t known report of a neoplasm in a capybara.