A Fibrosarcoma inthe SkeletalMuscle of a Capybara (Hydrochoerus hydrochaens)

An 8-yr-old male capybara (Hy- drochoerus hydrochaeris ), a resident of an ur- ban zoological collection in upstate New York (USA), had a mass posteroventral to its left stifle; it was of unknown duration. The mass was a fibrosarcoma based on invasive sheets of inter- woven spindle-shaped neoplastic cells with moderate associated extracellular matrix com- posed of collagen fibers. Supportive immuno- histochemical staining was positive for vimentin but negative for cytokeratins, desmin, and my- oglobin. The animal subsequently died of un- known causes. This is the first known report of