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 accounts for 17% of intestinal tumours in cats.

Signalment

• Dogs:
  • Mean age: 6-9 years
  • Minor male predisposition
  • Large breeds may predominate particularly collies and 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, or 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 and 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:

• Neutrophilic leukocytosis
• Monocytosis
• Eosinophilia
• Cutaneous disease
• Hyperviscosity syndromes

Physical Examination

• An abdominal mass may be palpable
• A rectal and potentially a lower colonic mass may also be palpable digitally via rectal examination
• Cats may also 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 cats, adenocarcinomas have been described as being of mixed echogenicity and are often asymmetric
• In dogs, adenocarcinomas have been described as being usually hypoechoic and most dogs had reduced gut motility

Endoscopy and Laparoscopy

Allow visualisation of the lesion. In addition, biopsies may be taken at this time, however, only small superficial samples can be obtained thus there can be significant variation in the interepretation of the findings. Open

Exploratory Laparotomy

If it has not been possible to make a definitive diagnosis using the above techniques then surgery is required. All abdominal tissues should be assessed and full thickness biopsies should be taken. Resection of the mass and intestinal anastomosis may be performed at this time.

Treatment

Surgery

Resection and anastamosis is advised as primary treatment for intestinal adenocarcinoma. Complete excision can usually achieved, however extraserosal invasion or adhesions may cause difficulties. In the small intestine, stapling and suturing by hand have been shown to be equally efficient. 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. Perioperative complications include peritonitis and sepsis. 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. With large intestinal adenocarcinoma survival time after surgery alone has been reported as approximately 4.5 months.

Adjuvant Chemotherapy

Doxirubicin has been shown to significantly improve survival times for cats with colonic adenocarcinoma with median survival times 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.

Radiotherapy

Rarely reported due to concerns of intolerance of surrounding tissues, in addition it cannot be relied upon that the same target will be irradiated each day due to intestinal mobility.

Prognosis

If no metastasis has occurred long term survival may be achieved following excision of the 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.

References

• Withrow S.J, Vail D.M (2007), Cancer of the Gastrointestinal Tract, in Withrow and MacEwen's Small Animal Clinical Oncology, fourth edition, Missouri, Saunders Elsevier, pp 491-501