Intestinal Adenocarcinoma

Introduction

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, they 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 occurrence is 6 to 9 years in the dog, and 10 to 12 years in the cat. There appears to be a predisposition in 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 mucus. 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 if it is large enough. 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 leiomyosarcoma and pancreatitis.

Laboratory Tests

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 be seen with intestinal obstruction, and blood urea nitrogen may be raised due to absorption following intestinal bleeding or dehydration. A test for faecal occult blood may be positive.

Diagnostic Imaging

It may be possible to visualise an abdominal mass with plain radiography, or dilated loops of small intestine may be seen, suggesting obstruction. Contrast radiography may be useful for localising filling defects of intraluminal space-occupying lesions or constrictions, particularly if gas accumulation makes ultrasonography difficult. Thoracic radiography is also recommended during diagnosis to detect pulmonary metastasis.

Abdominal ultrasonography is more sensitive than radiography in localising a mass and can assess the involvement of surrounding structures. In addition, thickness and layering of the intestinal wall can be evaluated: dogs with loss of layering are over 50 times more likely to have neoplastic disease rather than enteritis. Canine intestinal adenocarcinomas usually appear ultrasonographically as hypoechoic masses, and affected dogs have reduced gut motility. In contrast, feline intestinal adenocarcinomas are typically of mixed echogenicity and are often asymmetric.

Endoscopy

As wells as permitting visualisation of the lesion, endoscopy allows biopsies of the mass to be taken. Open proctoscopes are more useful than fibre optic scopes for colorectal lesions as direct visualisation of the mass is possible and deeper biopsies can be obtained. Nevertheless, endoscopic biopsy obtains only small superficial samples and so there can be significant variation in the interpretation of the findings.

Biopsy

Ultrasound guided fine needle aspirate of the mass or an enlarged lymph node may yield neoplastic epithelial cells on cytology, ruling out lymphoma. Since tumours are often deep to the mucosal surface, endoscopic biopsy frequently does not provide adequate information to make a diagnosis. Therefore, exploratory laparotomy and a surgical biopsy are required for a definitive diagnosis.

Treatment

Surgical resection and anastomosis is the treatment of choice for both small and large intestinal adenocarcinoma. For small intestinal lesions, a margin of 4-8cm is resected, and anastomosis may be achieved by suturing or stapling with no difference in outcome. Extraserosal invasion or adhesions may cause difficulties during resection and, for duodenal lesions, care must be taken to ensure there is no iatrogenic damage to the biliary or pancreatic ducts. Regional lymph nodes should be removed if there is evidence of metastasis. For colorectal adenocarcinomas, large margins may be more difficult to achieve due to restricted access. Transcolonic debulking is a palliative alternative for obstructive large intestinal lesions. For all types of surgery, postoperative complications include peritonitis and sepsis.

Adjunctive chemotherapy in the form of doxirubicin has been shown to significantly improve survival times for cats with colonic adenocarcinoma, with median survival times improved from 56 to 280 days when doxorubicin treatment was used. No other evidence exists to confirm the benefits of adjuvant chemotherapy in dogs or cats. Piroxicam, a non-steroidal anti-inflammatory drug may have palliative effects for large intestinal and rectal lesions.

The use of radiotherapy in intestinal adenocarcinoma has not been subject to detailed investigations due to the relative intolerance of the surrounding tissues to radiation. As well as the potential to cause intestinal perforations or adhesions, intestinal motility means that there is no certainty the same target will be irradiated each day. In a report of single high-dose irradiation used against a surgically-exposed anorectal tumour, no long-term side effects were observed.

Stool softeners may be useful in cases where an annular tumour causes constriction of the bowel lumen.

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%.

In dogs, the overall prognosis is poor. Animals with pedunculated rectal adenocarcinomas have a better prognosis than other tumour locations or forms, but for all tumours many cases recur locally or experience metastasis. Without surgical intervention, the median survival of dogs with small intestinal adenocarcinoma is 12 days, and following resection this is improved to around 10 months. A pedunculated colorectal adenocarcinoma has a median survival time of 32 months after excision, but annular tumours have a much worse prognosis with a survival of around 1.6 months.

There is significant perioperative risk associated with cats with small intestinal 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, and survival of over one year has been reported in small intestinal cases.

In order to track the progress of disease, it is recommended that animals undergo a full clinical examination, thoracic radiography and abdominal ultrasound at 1, 3, 6, 9 and 12 months post-surgery.

Links

• Proceedings of the World Small Animal Veterinary Association Congress 2001 - Update on Canine and Feline Gastrointestinal Neoplasia
• The Merck Veterinary Manual - Gastrointestinal Neoplasia

Intestinal Adenocarcinoma Learning Resources
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References

• Liptak J. M, Withrow S.J. (2007) Cancer of the Gastrointestinal Tract, in Withrow and MacEwen's Small Animal Clinical Oncology, (Fourth Edition) Saunders Elsevier.
• Tilley, L.P. and Smith, F.W.K.(2007) The 5-minute Veterinary Consult (Fourth Edition) Blackwell Publishing.
• White, R. A. S. (2003) Tumours of the intestines, in BSAVA Manual of Canine and Feline Oncology, (Second Edition) British Small Animal Veterinary Association.

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