Intestinal Adenocarcinoma

Intestinal tumours are uncommon accounting for less than 10% of all tumours in dogs and cats and 22% of gastrointestinal tumours in dogs and 35% in cats. It has been reported that the jejunum, ileum and caecum are the most frequent sites affected in the dog. Intestinal tumours in dogs and cats are usually malignant, Adenocarcinoma/carcinoma being the most common malignant tumour in dogs and accounting for 17% of intestinal tumours in cats.

Signalment

• Dogs:
  • Mean age: 6-9 years
  • Minor male predisposition
  • Large breeds may predominate particularly Collies, German Sheperds and Boxers

• Cats:
  • Mean age: 10-12 years
  • There are conflicting reports of whether there is a minor male predisposition
  • Siamese may have a breed predisposition

Description

• No organism or chemical agent has been identified that will induce spontaneous intestinal adenocarcinoma.
• The gross appearance of colorectal adenocarcinomas vary from pedunculated, particularly in the distal rectum, cobblestone, in particularly the middle rectum, and annular, also usually in the middle recutum, and may also have associations with tumour behaviour and prognosis.
• In cats, adenocarcinomas have been reported to have been found in the ileum and ileocaecal region. Another study reports the jejunum to be the most common site.
• Metastasis occurs via lymphatic and vascular routes. For small intestinal adenocarcinomas the most frequent sites of metastasis are the mesenteric lymph nodes. Other sites include the liver, kidneys, peritoneal cavity, omentum and lungs. Metastatic spread is commonly encountered at time of diagnosis.
• Large intestinal adenocarcinomas often metastasise to the deep inguinal lymph nodes. The liver is less frequently affected. These tumours also undergo aggressive local growth and local recurrence after resection frequently occurs.

Diagnosis

Clinical Signs

Usually chronic and often dependent on the site of the tumour within the gastrointestinal tract. Signs include:

• For more proximal lesions:
  • Vomiting
• For lesions within the small intestine:
  • Weight loss
• For tumours in the more distal tract:
  • Tenesmus
  • Hematochezia
  • Faeces may be altered in shape with constricting lesions
• Other signs reported include:
  • Anorexia
  • Diarrhoea
  • Signs associated with acute intestinal obstruction (usually when the tumour has grown in an annular form), perforation and peritonitis

Associated paraneoplastic abnormalities include:

• Neutrophilia
• Monocytosis
• Eosinophilia
• Cutaneous disease
• Hyperviscosity syndromes

Physical Examination

• An abdominal mass may be palpable
• A rectal mass, and potentially a lower colonic lesion, may be palpable digitally via rectal examination
• Cats may be dehydrated

Haematology and Biochemistry

Abnormalities observed include:

• Anaemia
• Leukocytosis
• Left shift
• Monocytosis
• Hypoproteinemia
• Raised hepatic enzymes
• High cholesterol
• Raised BUN - may be due to concurrent renal insufficiency, dehydration or absorption following intestinal bleeding
• Electrolyte abnormalities - due to intestinal obstruction

Abdominal Radiography

• An abdominal mass may be visible with plain radiography
• Alternatively, evidence of obstruction may be observed
• Poor serosal detail may be apparent
• Contrast radiography can be useful for localising masses, revealing obstructions and filling defects and for intestinal areas more difficult to visualise via ultrasonography due to the accumulation of air.

Thoracic Radiography

This is highly advised though presentation with pulmonary metastasis is infrequent.

Abdominal Ultrasonography

Is more sensitive than radiography in localising a mass and can assess involvement of surrounding structures. In addition, guided needle aspiration or biopsy may be taken at this time. Findings may include the following:

• Intestinal wall thickening with loss of wall layering - dogs with loss of layering are over 50 times more likely to have neoplastic disease rather than enteritis
• In dogs, adenocarcinomas have been described as being usually hypoechoic and most dogs have reduced gut motility
• In cats, adenocarcinomas have been described as being of mixed echogenicity and are often asymmetric

Endoscopy and Laparoscopy

Allow visualisation of the lesion. In addition, biopsies may be taken at this time. Open proctoscopes are more useful than fibreoptic scopes for colorectal lesions as direct visualisation of the mass is possible and deeper biopsies can be obtained. Nevertheless, often only small superficial samples can be obtained on biopsying the gut thus there can be significant variation in the interepretation of the findings.

Exploratory Laparotomy

Definitive diagnosis requires an excisional biopsy. All abdominal tissues should be assessed and full thickness biopsies taken. Resection of the mass and intestinal anastomosis may be performed at this time.

Treatment

Surgery

Surgical excision is advised as primary treatment for intestinal adenocarcinoma. Extraserosal invasion or adhesions may cause difficulties and care must be taken to ensure there is no iatrogenic damage to the biliary and pancreatic ducts for duodenal lesions. In the small intestine, wide local resection (4-8cm margins) can usually be achieved via enterectomy and anastomosis. Stapling and suturing by hand have been shown to be equally efficient for this procedure. If appropriate, regional lymph nodes should also be removed. Large margins may be more difficult to achieve for colorectal lesions due to access issues. Perioperative complications include peritonitis and sepsis.

Adjuvant Chemotherapy

Doxirubicin has been shown to significantly improve survival times for cats with colonic adenocarcinoma with median durations of 56 and 280 days for those not receving and those receiving chemotherapy respectively. No other evidence exists to confirm the benefits of adjuvant chemotherapy in dogs or cats. Piroxicam, a non-steroidal anti-inflammatory drug may have beneficial effects for rectal malignancy.

Radiotherapy

Rarely reported due to concerns of intolerance of surrounding tissues leading to for example perforations and adhesions, in addition it cannot be relied upon that the same target will be irradiated each day due to intestinal mobility. There has been a report of single high-dose iradiation being used for anorectal adenocarcinomas which had been surgically exposed and no long-term side effects were observed.

Prognosis

If no metastasis has occurred long term survival may be achieved following wide excision of a well differentiated small intestinal tumour. The rate of metastasis of adenocarcinoma to the local lymph nodes for both dogs and cats is approximately 50%. Without surgical intervention the mean survival of dogs with small intestinal adenocarcinoma is 12 days and reports varying from 114 days to 7-10 months with surgical treatment. Intensity of treatment is prognostic for colorectal tumours with palliative care carrying a poorer prognosis than local excision. In one study males with small intestinal adenocarcinoma had a significantly better prognosis than females with the same disease though the sample size was small. Local excision of colorectal adenocarcinoma has a median survival time of 22 months while the use of stool softeners alone has a median survival time of 15 months.

There is significant perioperative risk associated with cats with small intestine adenocarcinoma with a high mortality rate within the first two weeks following surgery. However, after these two weeks long term control may be achieved. For cats with large intestinal adenocarcinoma survival time after surgery alone has been reported as approximately 4.5 months.

References

• Liptak J. M, Withrow S.J, (2007), Cancer of the Gastrointestinal Tract, in Withrow and MacEwen's Small Animal Clinical Oncology, fourth edition, Eds Withrow S.J, Vail D.M, Missouri, Saunders Elsevier, pp 491-501
• White, R. A. S, (2003), Tumours of the intestines, in BSAVA Manual of Canine and Feline Oncology, second edition, Eds Dobson J. M, Lascelles B. D. X, Gloucester, British Small Animal Veterinary Association, pp 229-233