Myxoid Leiomyosarcoma of the Gizzard in a Broiler Chicken

A leiomyosarcoma was found in the gizzard of a 57-day-old female broiler chicken weighing 1.8 kg. Grossly, the tumor mass, 13.0 × 8.5 × 10.0 cm, enveloped the gizzard and had a gelatinous appearance due to the rich production of mucin. Miliary metastatic tumors were noted in the liver. Histopathologically, there was marked production of mucus throughout the tumor tissue, and densely or loosely arranged long spindle-shaped leiomyosarcoma cells proliferated. The tumor cells had a low rate of mitosis, showed slight cellular atypia, and, immunohistochemically, were positive for actin, α-smooth muscle actin, and desmin. Electron microscopically, various amounts of microfibrils with focal densities, dense patches, and basal plates were observed.