Fibrosarcoma on the leg of an adult rhesus macaque (Macaca mulatta)

This case describes a fibrosarcoma on the left upper leg of an adult female rhesus macaque. The patient was initially presented with a defined swelling at the caudolateral side of the upper leg. Medially from the growth, a swollen circular wound had formed with a fistula leading in the direction of the mass. The swelling was firm on palpation and was located in the subcutis, attached to the skin and underlying tissues. No other clinical abnormalities were observed. Treatment was initiated for an abscess with concurrent infection. Unfortunately, despite intensive wound debridement, wound lavage and antibiotic treatment, the growth did not resolve, and the animal was euthanased humanely due to clinical deterioration. Postmortem examination revealed a uniform, firm, white structure that had infiltrated deep into the underlying tissues. Histologically, the mass consisted of pleiomorphic spindle cells in fascicles with a collagenous stroma and negative desmin immunostaining, suggesting diagnosis of a fibrosarcoma.