Colonic adenocarcinoma with osseous metaplasia and systemic metastasis in a horse.

A 12-year-old thoroughbred mare was presented with colic and diarrhea. Clinical examination revealed mild tachycardia with injected mucous membranes. Abdominal ultrasonography identified thickened colon walls, an irregular, mottled liver, and free fluid. The mare had elevated liver enzymes and electrolyte abnormalities that continued to worsen during hospitalization and included hypoalbuminemia. Despite intensive and varied medical treatments, the mare's condition deteriorated and she was humanely euthanized. Postmortem examination revealed a large adenocarcinoma with osseous metaplasia in the right dorsal colon and mesocolon with multifocal metastasis.