38 Colorectal neoplasia in a dog

Initial presentation

Haematochezia, diarrhoea and faecal tenesmus

Signalment: 2-year-old entire male German shepherd dog, body weight

29 kg

Case history

The dog had initially begun to have diarrhoea 4 months prior to present­ation.

His current diet was a restricted protein dry diet, with no snacks or treats. The dog’s vaccinations were current and he had recently been treated with 50 mg/kg fenbendazole for 5 days.

He was on meloxicam for discomfort due to hip dysplasia. This had been stopped for a month 2 months earlier and there had been no resol­ution of clinical signs of diarrhoea or haematochezia. Other than the hip dysplasia, he had been a healthy dog until the onset of the diarrhoea.

Physical examination

The dog was bright, alert and responsive (Fig 38.1) although he was quite thin (body condition score 3/9) with muscle loss over the lumbar area (Fig 38.2). His mucous membranes were pink and moist with a ca­pillary refill time of resolved within a week of initiation of this treatment and the haematochezia decreased with the chemotherapy.

At 1 month after diagnosis the dog was reported to have gained 1 kg in weight. There was no organomegaly present, although there was a persistent caudal abdominal lymphadenopathy. On digital rectal exam­ination the previous mass could not be felt. The dog’s faeces were soft but formed and no blood was present. His status was described as partial remission. At 4 months after diagnosis the dog was doing very well and had gained another 3 kg in weight.

Discussion and epidemiology

Colorectal tumours are uncommon in dogs. The most common tumours in this location are adenomas or adenocarcinomas, which often have a more rounded appearance than this tumour (Fig 38.6) and are often found as a focal growth which does not metastasize. Adenomas and ad­enocarcinomas are most often tumours of older dogs. If not surgically

resectable, the clinical signs from adenomas and adenocarcinomas often improve with the use of NSAIDs, such as piroxicam given as rectal sup­positories or per os.

Fig 38.6

Endoscopic picture of a colonic adenoma

Alimentary lymphoma accounts for about 5% of cases of lymphoma and is often more difficult to diagnose than the more common multi­centric form. In this dog, the presence of a colorectal lymphoma was not definitively proven, although he had lymph node involvement. This could either be a spread of the colorectal tumour or the dog may have had two diseases. In one study, the median age for GI lymphoma was about 8 years, with a spread of about 3 to 13 years, so this dog was a fairly young victim of the disease. Six of 30 dogs in that study had en­larged lymph nodes.

There appears to be no clear sex predilection for lymphoma, although some studies have shown more male than female dogs affected.

Prednisolone was used in this dog prior to the initiation of a chemo­therapy protocol. Most oncologists have recommended against using glucocorticoids for treating dogs suspected of having lymphoma. If the lymphoma has not been diagnosed, the rapid Iymphocytolytic effects of glucocorticoids may have masked the diagnosis. Another reason for avoiding corticosteroid USC is the potential of multidrug resistance (MDR). MDR is a common cause for chemotherapeutic failure in canine lymphoma. It involves P-glycoprotein, a transmembrane protein which acts as an efflux pump for some chemotherapeutic agents, causing the drugs to be extruded from the tumour cells.

Prognosis

In one study the overall median survival time of dogs with GI lymphoma was 13 days; however, two dogs were alive at 31 and 84 months and both of these dogs had colonic or rectal neoplasia. Overall, alimentary lymphoma provides a fair prognosis for short to medium term remission, but a guarded prognosis for a long remission.