A 3-yr-old male inland bearded dragon (Pogona vitticeps) presented for progressive right forelimb lameness of 3-wk duration, anorexia, dyspnea with increased lung sounds, open–mouth-breathing, and compulsive neck thrashing. The owners opted for euthanasia. Necropsy revealed a yellow, opaque, soft tissue mass in the right axillary region dorsal to the brachial plexus. This round focal mass was well demarcated, measuring 1.3 cm in diameter, 0.4 cm in height, and incorporated a large unidentified blood vessel. Histopathology revealed an expansile, infiltrative, unencapsulated, poorly demarcated mass composed of neoplastic spindle cells forming streams and bundles separating adjacent muscle fascicles and infiltrating into surrounding vertebral bone and extending into a bone process. These spindle cells exhibited eosinophilic to amphophilic cytoplasm and a round to oval nucleus with finely stippled chromatin and a mitotic rate of 23 per 10 high-power fields. Immunohistochemistry (smooth muscle actin) identified the mass as a leiomyosarcoma. Despite local neoplastic infiltrates into the surrounding vertebral bone, there were no systemic metastases discovered grossly or on histopathology. The lungs exhibited interstitial mixed inflammation alongside mineralization and edema within the respiratory parenchyma consistent with interstitial pneumonia, which was believed to be the reason for the respiratory signs. This is the first report of an axillary leiomyosarcoma in a reptile and represents an unusual differential for unilateral lameness.

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