What is your diagnosis? Carcinoma in a horse.

The research article discusses a case involving a 28-year-old Quarter Horse gelding diagnosed with metastatic carcinoma, a rare cancer condition generally found in horses. The horse, initially evaluated for colic, displayed symptoms of high heart and respiratory rates, held an extended neck posture and reluctance to move, which later linked to the eventual diagnosis.

History and Initial Evaluation

• The horse was examined due to an episode of colic lasting a day.
• Prior to the episode, the horse suffered from a neck injury when it pulled back on its crossties.
• Initial assessment showed increased heart and respiratory rates, with the horse displaying reluctance to move its neck and presenting with an ataxic gait, especially in the hind limbs.
• There was also a noticeable swelling on the left side of the horse’s neck, specifically over the C2 to C5 vertebral region.

Radiographic Findings and Interpretation

• Radiographic images revealed well-circumscribed osteolytic vertebral lesions, mainly in the dorsal area of the C2 spinous process.
• Two smaller lesions were found in the caudal ventral region of C3 and the cranial area of C4’s vertebral body.
• Due to the polyostotic osteolytic vertebral lesions observed, a diagnosis of either round cell neoplasia or metastatic neoplasia was suggested.

Treatment and Outcome

• Owing to the high likelihood of neoplasia and deteriorating health condition, the horse was euthanized.
• A biopsy performed post-euthanasia identified an ovoid, non-encapsulated fibrous mass replacing the normal cancellous bone in the C2 dorsal spinous process.
• The histopathological study of the tumor cells indicated a metastatic origin to the bone lesions.
• The final diagnosis confirmed metastatic carcinoma. However, due to the owner’s request, a necropsy was not conducted, and the primary tumor could not be identified.

Discussion and Observations

• The polyostotic vertebral lesions found in the horse showed both aggressive and non-aggressive features.
• Neoplastic invasion of vertebral bodies has the potential to cause osteomalacia and pathological fractures.
• Signs of colic were likely a result of referred pain, and the high lactate concentration in the blood could be due to a decrease in tissue perfusion.
• Though bone neoplasms are rare in horses, when they do occur, they are more common in the axial skeleton than in the appendicular skeleton.
• While lymphosarcoma is one of the more commonly found cancers in horses, in this case, a primary carcinoma was given higher likelihood due to the epithelial nature of the tumor cells.