Pleomorphic Leiomyosarcoma in the Hind Leg of a Taiwanese Macaque (Macaca Cyclopis)

An adult, captive Taiwanese monkey (Macaca cyclopis) presented clinically with a large, rapidly growing mass located in the crus of the left hind leg. The overlying skin was severely ulcerated and necrotic. Radiographs suggested an invasive neoplasm in soft tissue with no bone involvement. The animal's clinical condition progressively worsened over the next 3 months until it died. Necropsy revealed that the mass infiltrated the surrounding skeletal muscle with no evidence of distant metastasis. Microscopically, the mass was highly cellular and composed of round to spindle cells with frequent rhabdoid cells characterized by abundant eosinophilic glassy cytoplasmic inclusions and large, bizarre nuclei. Phosphotungstic acid hematoxylin staining failed to reveal distinct cross-striations within the neoplastic cells. Neoplastic cells were strongly positive for smooth muscle actin and vimentin but were negative for sarcomeric actin, myoglobin, desmin, cytokeratin, S100, and lysozyme. The gross, microscopic, and immunohistochemical findings supported the diagnosis of pleomorphic leiomyosarcoma.