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

Colonic adenocarcinoma with osseous metaplasia caused severe illness in a 12-year-old horse, leading to systemic metastasis and necessitating euthanasia. The study describes the clinical signs, diagnostic findings, treatment efforts, and postmortem results in this equine case.

Case Presentation and Clinical Findings

• A 12-year-old thoroughbred mare exhibited symptoms of colic and diarrhea, prompting veterinary evaluation.
• Initial clinical examination found mild tachycardia (increased heart rate) and injected (congested) mucous membranes, indicating possible systemic disease or inflammation.
• Abdominal ultrasonography revealed:
• Thickened walls of the colon, suggesting inflammation or tumor presence.
• An irregular, mottled appearance of the liver, indicating possible hepatic involvement or secondary effects.
• Presence of free fluid in the abdomen, which may signal inflammation, infection, or neoplastic effusion.
• Bloodwork showed elevated liver enzymes, pointing to liver damage or stress, and electrolyte abnormalities, including hypoalbuminemia (low blood albumin), signifying impaired protein production or systemic illness.

Treatment and Clinical Course

• The mare received intensive and varied medical treatments aimed at addressing the colic, diarrhea, liver abnormalities, and electrolyte imbalances.
• Despite these interventions, the mare’s clinical condition worsened progressively during hospitalization.
• Persistent hypoalbuminemia and deteriorating liver function markers underscored ongoing systemic compromise.
• Due to poor prognosis and declining health, the decision was made to humanely euthanize the mare.

Postmortem Examination and Diagnosis

• Necropsy identified a large adenocarcinoma located in the right dorsal colon and mesocolon.
• The tumor exhibited osseous metaplasia – an abnormal transformation where bone tissue forms within the carcinoma, a rare finding in equine colon cancers.
• Multifocal metastases were found, indicating that cancer cells had spread to multiple sites beyond the primary tumor location.
• The presence of systemic metastasis explains the wide-ranging clinical signs and poor response to treatment.

Significance and Implications

• This case highlights a rare presentation of colonic adenocarcinoma with osseous metaplasia in a horse, an unusual pathology in equine medicine.
• It demonstrates the challenges in diagnosing and managing neoplastic diseases presenting with gastrointestinal and hepatic symptoms in horses.
• Early recognition of such tumors is difficult given the nonspecific clinical signs like colic and diarrhea.
• The report underscores the importance of thorough diagnostic imaging and postmortem examination to provide definitive diagnoses for complex cases.
• Knowledge gained from such cases can assist veterinarians in better identifying and managing similar conditions in future equine patients.