Gastric Neoplasia - Dog and Cat

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

• Adenocarcinoma - 70-80% of cancers of the somach in dogs
• Squamous Cell Carcinoma
• Lymphoma - the most common gastric neoplasm in the cat
• 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 carinoma - 8 years
• Cats with carcinoma - usually over 10 years
• Mean age of dogs with benign tumour - 15 years

Description

Aetiology largely idiopathic though long term ingestion of dietary carcinogens may have some responsibility. Long term administration of nitrosamines may cause carcinomas in dogs. In humans, the bacterium Helicobacter pylori can induce gastric carcinoma and lymphoma. Its role in gastric tumours in dogs and cats has not yet been fully established though it can cause gastritis and ulceration. Belgian Shepher dogs may have a genetic predisposition to gastric carcinoma. Cats with gastric lymphoma 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 and peritonitis. Other complications include:

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

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

Diagnosis

History and Clinical Signs

• May ne 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 resulting 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

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 focal outpouching of the luminal (inner) surface with trapped gas bubbles. guided fine-neelde or core biopsies may be taken at this time.

Endoscopy and Biopsy

This allows direct visualisation of the lesion. Definitive diagnosis requires histolpathology. 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.

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 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, there are often difficulties as tumours are often in an advanced stage on 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 injury to the local blood supply as well as 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 unresectable.

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.