Intestinal Adenocarcinoma

Description

Intestinal adenocarcinomas are a reasonably common malignant neoplasm of dogs and cats arising from the epithelial lining of the gastrointesinal tract. As yet, no causative organism or chemical agent has been identified for intestinal adenocarcinomas, but experiments have suggested that nitrosamines may have a role. Intestinal adenocarcinomas can be nodular or annular in appearance. By the time of diagnosis, intestinal adenocarcinomas have often metastasised via the lymphatic and vascular routes, most commonly to the mesenteric lymph nodes. Other sites of metastasis include the liver, kidneys, peritoneal cavity, omentum and lungs. Intestinal adenocarcinomas display aggressive local growth and invasion, and tumours frequently recur after resection.

Signalment

Dogs are more commonly afflicted with intestinal adenocarcinoma than cats. Intestinal adenocarcinomas have been seen in animals between the ages of 3 and 13 years, but most cases are seen in middle aged to older animals. The mean age of occurence is 6 to 9 years in the dog, and 10 to 12 years in the cat. There apppears to be a predisposition for males, and this is more pronounced in dogs than in cats. There are no breed predispositions.

Diagnosis

Clinical Signs

Dogs and cats present with a history of gastrointestinal signs. Tumours of the small intestine are associated with vomiting, weight loss, melaena, flatulence and borborygmus, and large intestinal adenocarcinoma can cause haematochezia with tenesmus and mucous. Constricting lesions in the distal tract may also change the shape of the faeces passed. Other signs reported in either form include anorexia, diarrhoea and signs associated with acute intestinal obstruction or perforation and peritonitis.

Small intestinal adenocarcinomas may be palpable transabdominally as a mid-abdominal mass. Distended loops of small intestine may also be palpated, and rectal examination may reveal melaena. A mass may be palpated per rectum in large intestinal adenocarcinomas. This may present as a constriction or as nodular lesions protruding into the lumen. Bright red blood may be discovered on rectal examination.

Various paraneoplastic syndromes have been associated with intestinal adenocarcinoma, including cutaneous disease and hyperviscosity syndromes.

Differential diagnoses for intestinal adenocarcinoma include: intestinal foreign body, inflammatory bowel disease, alimentary lymphoma, gastrointestinal parasitism, leiomyoma or meiomyosarcoma and pancreatitis.

Laboratory Test

Haematology often reveals a microcytic, hypochromic anaemia from chronic bleeding to the gastrointestinal tract. The loss of whole blood may also lead to hypoproteinemia on routine biochemistry. Electrolyte abnormalities may bee seen with intestinal obstruction, and blood urea nitrogen may be raised due to absorbtion following intestinal bleeding or dehydration. A test for faecal occult blood may be positive.

Diagnostic Imaging

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

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 lesions.

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 irradiation 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 for those who receive surgical treatment. 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. Intensity of treatment is prognostic for colorectal tumours with palliative care carrying a poorer prognosis than local excision. 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