What is your diagnosis? Biopsy impression smear of a hepatic mass in a yearling Thoroughbred filly.

This research details the presentation, diagnosis, treatment, and post-mortem findings of a rare case of hepatoblastoma, a type of liver cancer, in a young racehorse, whose symptoms included abnormally high levels of red blood cells, higher-than-normal protein in the blood, and increased levels of certain enzymes indicative of liver damage. The unique aspects of this case include secondary erythrocytosis caused by excessive production of erythropoietin by the tumor, something not previously documented in equine medical literature.

Case Presentation

• The patient was a 1-year-old Thoroughbred filly, presenting symptoms such as fever, lack of appetite, reduced water intake, and diarrhea over a period of 10 days. Initial investigations done by the referring vet revealed erythrocytosis (abnormally high red blood cell count), hyperproteinemia (excess protein in the blood), and increased activity of enzymatic markers that typically indicate liver damage or disease (gamma-glutamyltransferase and lactate dehydrogenase).

Clinical Findings and Investigations

• A review of the patient’s condition at the Cornell University veterinary hospital confirmed the prior clinical findings and added thrombocytosis (increased platelet count) and hypoglycemia (low blood sugar) to the list of conditions. Despite administration of fluids, the high red blood cell count persisted.
• An ultrasound examination showed an abnormally enlarged liver along with a large hepatic mass measuring 21 x 25-cm with varied echogenicity, indicating a potential malignancy.

Biopsy and Cytology Results

• An ultrasound-guided biopsy of the liver mass showed a neoplastic epithelial population that did not resemble normal liver cells, prompting a suspicion of hepatoblastoma.

Final Diagnosis and Necropsy Findings

• The diagnosis of hepatoblastoma was confirmed upon histopathologic examination of the mass after necropsy.
• The necropsy also showed bone marrow erythroid hyperplasia, a condition where the bone marrow produces an excessive number of red blood cells.

Significant Findings

• The patient’s serum showed an erythropoietin concentration of 28.0 mU/mL, significantly higher than the reference range of 1.0-11.8 mU/mL. Erythropoietin is a hormone that stimulates the production of red blood cells, suggesting that the tumor was secreting this hormone, leading to secondary erythrocytosis.
• This case is notable for being the first that describes secondary erythrocytosis with high erythropoietin concentration in a horse with hepatoblastoma. Additionally, it’s the first to record the cytopathologic features of this tumor.