Cat & Dog - Digestive Tract Muscle and Connective Tissue 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.

What are these tumours?

Muscle (called 'smooth muscle') and fibrous connective tissues form the framework (stroma) that holds other tissues together in the organs of the body. They enable these organs to contract and stretch as part of their function, for example in digestion of food. A number of different tumours can develop from the cells of these tissues.

Granular cell tumours are rare, slow growing tumours, probably originating from primitive, precursor cells that have the ability to make many different types of connective tissue cells including muscle and fibrous tissue. This tumour is usually in the tongue and only one has ever been recorded as spreading (metastasising) so they are almost always benign (non-spreading).

Benign (leiomyoma) and malignant (leiomyosarcoma) tumours originate from the muscle of the digestive tract, usually in the stomach or intestines. They form nodules that obstruct the passage of food. Some contain fibrous tissue and some other tumours are formed only from fibrous tissue or from other supporting tissues such as nerves. Benign tumours end in '-oma' and malignant ones in '-sarcoma'.

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 culmination of a series of circumstances which come together for the unfortunate individual.

Cancer induction is a multistep process called tumour progression. Some cancers never progress past the first stages so remain benign. Others progress rapidly.

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 probable is a mutation so cancer is commoner in older animals.

Are these common tumours?

Granular cell tumours are uncommon in dogs but most common in the tongue with a mean age of 9 years. They are rare in cats.

Leiomyomas are rare but most common at the junction of the oesophagus (food pipe) and stomach. The tumours may be multiple. In the intestine they are usually solitary. Malignant tumours are even less common.

All the other stromal tumours are rare.

How will these cancers affect my pet?

Granular cell tumours are slow growing and because they cause so few problems, have often been present for years before removal.

Leiomyomas cause obstruction and ulceration of the gut. In the stomach they may be multiple but small tumours rarely cause clinical signs. In the intestine, they are usually solitary (on their own). Occasionally they bleed sufficiently to cause anaemia and blood in the faeces. Local inflammation of the inside lining of the abdomen (peritonitis) is present in up to half the cases. An unusual feature of these tumours is their ability to induce low blood sugar concentrations. This can produce clinical signs including weakness, confusion and collapse.

How is this cancer diagnosed?

Cancer is often suspected from the clinical signs. Radiographs (x-rays) may be useful in detecting abdominal tumours. Blood tests are not diagnostic but sometimes indicate low blood sugar or if the tumour is bleeding internally.

In order to identify the tumour, it is necessary to obtain a sample of the tumour itself. Small biopsies taken via an endoscope may not be diagnostic and a larger surgical specimen may need to be obtained by exploratory surgery. This is then examined by histopathology (microscopic examination of specially prepared and stained tissue sections). This is done at a specialised laboratory where the slides are examined by a veterinary pathologist. Examination of the whole lump will also indicate whether the cancer has been fully removed. Histopathology also rules out other more serious cancers.

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 one of these stages. The body's own immune system can kill cancer cells but it is rarely 100% effective. Rarely, reduced blood supply will make leiomyomas partly die and become fibrous. This may reduce the size of the cancer.

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 aid 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. Granular cell tumours are benign and usually cured by surgical removal.

Leiomyomas and leiomyosarcoma are a continuum from benign to malignant so prediction of behaviour is not always easy. However, although they may spread (metastasise), this is late in the disease and often only to the local lymph nodes (glands). The outlook is usually good following surgery.

Are there any risks to my family or other pets?

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