Gastric Neoplasia - Dog and Cat

More frequent compared with oesophageal neoplasia but still uncommon accounting for less than 1% of all malignancies. Malignant tumours include:

• Adenocarcinoma - 70-80% of all canine gastric neoplasms
• Squamous Cell Carcinoma
• Lymphoma - the most common feline gastric neoplasm
• Fribrosarcoma
• Plasmacytoma
• Leiomyosarcoma
• Mast cell
• Gastrointestinal stromal tumours (GIST tumours) - 20% of these tumours occur in the canine stomach

Benign tumours include:

• Polyps
• Leiomyoma

Signalment

• Male dogs are more commonly affected than female: e.g male:female ratio in those with carcinoma 2.5:1
• Mean age of dogs with carinomas - 8 years
• Cats with carcinomas - usually over 10 years
• Mean age of dogs with benign tumours - 15 years

Description

Aetiology largely idiopathic though long term ingestion of dietary carcinogens may have some responsibility. Long term administration of nitrosamines may also cause carcinomas in dogs. In humans, Helicobacter pylori can induce gastric carcinomas and lymphomas. Its role in gastric tumours in dogs and cats has not yet been fully established though it is known to cause gastritis and ulceration. Belgian Shepherd dogs may have a genetic predisposition to gastric carcinomas. Cats with gastric lymphomas are not usually FeLV positive.

Adenocarcinomas: frequently metastasise to the regional lymph nodes (gastroduodenal and splenic lymph nodes), also the liver and sometimes the lungs. They are also locally aggressive and can cause stomach wall perforation resulting in peritonitis. Other complications include:

• Pyloric outflow obstruction
• Ischaemic necrosis - where tumour plugs develop in the surrounding vasculature

Leiomyosarcomas: rarely metastasise. Lymphoma: may be limited to the stomach, may affect lymph nodes and other abdominal organs or may be multicentric. Plasmacytoma: metastasis is frequently evident in local lymph nodes.

Diagnosis

History and Clinical Signs

• May be mild or non-specific early on in the disease process
• Chronic vomiting - blood tinged/'coffee grounds' appearance (partially digested blood)
• Weight loss
• Anorexia
• Maleana/occult faecal blood
• Anterior abdominal pain may or may not be present

Haematology and biochemistry

• Regerative anaemia - on account of gastric haemorrhage
• Electrolyte disturbances - secondary to vomiting
• Elevated BUN and creatinine - due to dehydration
• Elevated hepatic enzymes - if hepatic metastasis has occured or if there is obstruction to the common bile duct.

Positive Contrast Radiography

The following abnormalities may be observed:

• Apparent mass extending into the gastric lumen
• Delayed gastric emptying
• Changes in motility in certain areas of the stomach
• Thickening of the gastric wall or ulceration
• Filling defects
• Loss of rugal folds

Ultrasonography and Biopsy

Characteristic features of gastric neoplasia are a thickened gastric wall along with disruption of the wall layers. Enlarged lymph nodes may be observed. The rest of the abdominal organs should be checked for metastases. Ulceration appears as a localised outpouching of the luminal (inner) surface with accompanying gas bubbles which become trapped. Definitive diagnosis requires histopathology of samples. Guided fine-needle or core biopsies may be taken at this time.

Endoscopy and Biopsy

This allows direct visualisation of the lesion. Several biopsies can be taken via grab biopsy, however the samples may be unrepresentative.

Surgical Biopsy

Alternatively, biopsies can be taken via gastrotomy at the time of surgical treatment (see below). If a GIST is susptected a CD117 immunohistochemical stain can be used for diagnosis (in half of all dogs affected GIST tumours express CD117 (c-kit), a tyrosine kinase receptor).

Paraneoplastic Syndromes

• Hypercalcaemia - may be associated with lymphoma
• Hypoglycaemia - can be associated with leiomyomas and leiomyosarcomas and is potentially reversibe following tumour resection.

Treatment

Surgery

Prior to any surgical intervention thoracic radiography should be performed for evidence of metastasis. Regional lymph nodes should also be examined at the start of surgery along with the rest of the abdominal cavity. For tumours that have not metastasised, resection is the treatment of choice (wide partial gastrectomy or antrectomy with gastroduodenostomy (Billroth 1). However, frequently there are difficulties as tumours are often in an advanced stage at time of presentation. Excision with large margins whilst maintaining the ability to sucessfully reconstruct the stomach without post-operative complications can be problematic. Futhermore, pylorectomy and gastroduodenostomy or gastrojejunostomy for antral tumours risk iatrogenic trauma to the local blood supply as well as to the pancreas and extrahepatic biliary system. Post-operative complications are more frequent with resections associated with the pylorus. Neoplasia associated with the lesser curvature is generally non-resectable.

Chemotherapy

For lymphoma only. There is an associated risk of gastric perforation.

Radiotherapy

Unreported. Surrounding tissues including the liver and intestine show poor tolerance.

Other Medical Management

Symptomatic therapy of for example vomiting may improve quality of life in the short term. Treatment options include anti-emetics such as metocolpramide and H2 blockers including ranitidine and cimetidine. Inhibitors of c-Kit e.g imatinib have been used in humans with GIST tumours. Such inhibitors may be useful for GIST in animals.

Prognosis

Variable:

• Benign tumours - Frequently cured by surgical resection. Prognosis good.
• Lymphoma - response to chemotherapy usually poor. Survival rates low.
• Most malignant tumours - usually associated with recurrent or metastatic cancer. Prognosis therefore usually poor despite surgical resection. Survival time up to six months.
• Extramedullary plasmacytomas - can have a very good prognosis following surgery and chemotherapy.

References

• Morris J, Dobson J (2001) Gastrointestinal Tract, in Small Animal Oncology, Blackwell Science, pp 127-130
• 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 480-482