Large B-cell lymphoma in the colon and mesocolon of a Thoroughbred racehorse: Detection prior to development of clinical signs using clinicopathological markers of inflammation

In this report, we describe an investigation into the cause of chronic inflammation in a clinically normal 5-year-old racing Thoroughbred, finally confirmed to be associated with B-cell lymphoma. Over a 14-week period, the horse was regularly evaluated by sequential blood testing, revealing persistent inflammation of unknown origin, unresponsive to treatment. Eventually, an abdominal mass was identified by transabdominal ultrasound and rectal palpation. Surgical exploration revealed an extensive, invasive soft tissue mass in the abdomen. At post-mortem examination, a mass involving the colon, mesocolon and mesocolonic lymph node was sampled and confirmed as a large B-cell lymphoma by histopathology and immunohistochemistry. In cases of unexplained chronic inflammation in a horse, neoplasia should be considered as a possible aetiology.

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