Cat & Dog - Stomach Tumours

These notes are provided to help you understand the diagnosis or possible diagnosis of cancer in your pet. For general information on cancer in pets ask for our handout What is cancer. If not already performed your veterinary surgeon may suggest certain tests to help confirm or eliminate the diagnosis, and to help assess treatment options and likely outcomes. Because individual situations and responses vary, and because cancers often behave unpredictably, science can only give us a guide. However information and understanding of tumours in animals is improving all the time.

We understand that this can be a very worrying time and we apologise for the need to use some technical language. If you do not understand anything, please do not hesitate to ask.

• Epithelium is a thin tissue layer which lines the stomach and gut.
• Glandular means that the tissue has glands contained within it, eg for acid secretion
• Gastric is anything related to the stomach eg gastric epithelium is stomach lining)
• Benign tumours are often slow growing and don't spread
• Malignant tumours are aggressive and spread to other parts of the body
• Histopathology is microscopic examination of specially prepared and stained tissue sections

What are these tumours?

Tumours of the epithelial, glandular stomach lining include non-cancerous polyps and some types of chronic (hyperplastic) gastritis. Malignant epithelial tumours (gastricadenocarcinomas) cause progressive illness. This usually starts only a few weeks before diagnosis but within that time, they have usually spread locally and to distant organs. Many recur following surgery.

What do we know about the cause?

The reason why a particular pet may develop this, or any cancer, is not straightforward. Cancer is often seemingly the result of a series of circumstances which come together for the unfortunate individual.

In people, the bacterium Helicobacter pylori is the cause of a spectrum of disease. This includes promoting the development of gastric adenocarcinoma. We do not know whether the same is true in dogs and cats, which also carry Helicobacter bacteria. Certain foods are implicated in these cancers in both people and farm animals and chemicals such as nitrosamines have been shown to induce gastric adenocarcinomas.

Why has my animal developed this cancer?

Some animals have a greater tendency (genetic susceptibility) to cancer. Some breeds have far more cancers than others, often of specific types. The more divisions a cell undergoes, the more likely a mutation is, so cancer is commoner in older animals.

Are these common tumours?

Benign stomach tumours are very rare. Malignant epithelial or glandular tumours (adenocarcinomas) occur more frequently, but are still uncommon in dogs and rare in cats.

How will these cancers affect my pet?

Vomiting, often not associated with food intake, and sometimes containing blood, occurs in almost all animals with gastric tumours. Other clinical signs are weight loss, loss of appetite, diarrhoea and blood in the faeces.

How are these cancers diagnosed?

Cancer is often suspected from the clinical signs. Radiographs (x-rays) may be useful in detecting the tumours. Blood tests are not diagnostic but sometimes indicate if the tumour is bleeding internally. In order to identify the tumour, it is necessary to obtain a sample of the tumour itself. Various degrees of surgical invasion may be needed such as endoscopy and exploratory surgery. The tissue samples are submitted for microscopic examination. Biopsies taken with the aid of an endoscope are rarely diagnostic for cancer and examination of a larger surgical specimen from deeper tissue is usually needed. The histopathology is done at a specialised laboratory where the slides are examined by a veterinary pathologist.

What types of treatment are available?

Treatment is surgical removal of the tumour.

Can these cancers disappear without treatment?

Cancer rarely disappears without treatment but as development is a multi-step process, it may stop at some stages, particularly if a promoting agent such as Helicobacter infection is removed. The body's own immune system can kill cancer cells but it is rarely 100% effective. Rarely, loss of blood supply to a cancer will make it die but the dead tissue will probably need surgical removal.

How can I nurse my pet?

After surgery, the operation site needs to be kept clean and your pet should not be allowed to interfere with the site. Any loss of sutures (stitches) or significant swelling or bleeding should be reported to your veterinary surgeon.

Your pet may require a special diet and you may be asked to check that your pet can pass urine and faeces or to give treatment to facilitate this.

If you require additional advice on post-surgical care, please ask.

How will I know how the cancer will behave?

Histopathology will give your veterinary surgeon the diagnosis that helps to indicate how it is likely to behave. The veterinary pathologist usually adds a prognosis that describes the probability of local recurrence or metastasis (distant spread).

When will I know if the cancer is permanently cured?

'Cure' has to be a guarded term in dealing with any cancer.

Gastric polyps are usually cured by surgical removal. They are thought to be non-precancerous (not capable of becoming cancer). Despite early diagnosis (often only weeks since illness was noted), unfortunately most gastric adenocarcinomas have spread locally at the time of surgery. Surgical removal is therefore difficult. They can also spread within the inside lining of the abdomen (peritoneum) and to many different parts of the body including the lungs. Despite this, post-surgical survival times have increased recently, rising from a few months to between one and three years.

Are there any risks to my family or other pets?

No, these tumours are not transmitted from pet to pet or from pets to people.