Cat & Dog - Neuroendocrine Tumours - Carcinoids

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 neuroendocrine cells?

Neuroendocrine cells interact with the nervous system and produce specialised chemical substances called 'neuroendocrine hormones'. These hormones affect the rates of specific chemical reactions in other cells locally or in other tissues of the body. Together with the nervous system and other types of hormones they integrate and co-ordinate a wide variety of activities to maintain internal stability of the body. The neuroendocrine hormone producing cells are present in glands such as the adrenal medulla, chemoreceptors (aortic and carotid bodies) and pancreatic islets. They are also scattered throughout the body in a variety of organs including the skin, mouth, oesophagus, intestine, liver and lung.

What are neuroendocrine tumours?

The scattered neuroendocrine cells produce rare tumours (carcinoids, Merkel cell tumours and neuroendocrine tumours). Merkel cells are present in epithelial (outer covering or lining) tissues. Tumours of these cells have been confirmed in the mouths of animals. Neuroendocrine tumours of the intestine, liver and gall bladder are called carcinoids and neuroendocrine carcinomas in the nose and lung are sometimes called 'small cell' carcinomas. Neuroendocrine tumours of the aortic or carotid bodies are called chemodectomas.  See handouts on Neuroendorine/chemoreceptor tumours.  In general, the tumours are slow growing but will eventually spread (metastasise) to other parts of the body.

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 is non-lethal genetic damage of cells (mutations in the DNA genome). Causes include radiation, chemicals, hormones and infections but we do not know if any of these is important in the development of these tumours. The mutated cells upset the normal regulation of cell death and replacement. They do this by activating growth-promoting cancer genes (oncogenes), inactivating suppressing genes and altering the genes that regulate normal, programmed cell death (apoptosis). Cancer induction is a multi-step 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?

These are all rare tumours, primarily recognised in dogs and very infrequent in cats. They may be more common than we realise, however, because confirmation of the diagnosis requires specialised and expensive microscopic techniques and sometimes electron microscopy. Some types recognised in people have not yet been identified in domestic animals.

How will these cancers affect my pet?

Most of these tumours do not produce hormones so clinical problems are primarily associated with their size and compression of the adjacent tissues.

A few of the tumours induce signs that are not readily explained by local or distant spread of the tumours. These are known as 'paraneoplastic syndromes'  Some are due to abnormal hormone production by the cancer.  In people, several different types are recognised and in animals, hair loss and increased blood calcium levels are thought to occur.

How are these cancers diagnosed?

Clinical signs of these tumours relate to the organ affected. Further specialized diagnostic techniques may include radiographs (x-rays), ultrasonography and CT (computerised tomography) scans and MRI (magnetic resonance imaging). These can often provide a high probability of the presence of a tumour but definitive diagnosis of the type relies on microscopic examination of tissue (histopathology). Routine histopathology, done at a specialised laboratory by a veterinary pathologist, will give a high probability of diagnosis. Confirmation may require many different stains (immunocytochemistry) to eliminate other tumours or electron microscopy. These are expensive techniques and not routinely available.

The piece of tissue may be a small part of the mass (biopsy) or the whole lump but only examination of the whole lump will indicate whether the cancer has been fully removed. The histopathology helps to predict behaviour (prognosis).

What types of treatment are available?

Treatment is surgical removal of the lump(s). Radiotherapy is occasionally used for nasal tumours.

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. 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 this is rarely complete.

How can I nurse my pet?

After surgery, you will need to prevent your pet from interfering with the operation site and an "Elizabethan collar" may be needed. The site also needs to be kept clean. Any loss of stitches or significant swelling or bleeding should be reported to your veterinary surgeon. 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 the tumour is likely to behave. The veterinary pathologist usually adds a prognosis that describes the probability of local recurrence or metastasis (distant spread).

How will I know if the cancer is permanently cured?

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

Most of these tumours grow slowly but eventually invade and destroy adjacent structures.

Neuroendocrine carcinomas in the nose tend to invade the brain. An overall metastasis rate of 41 per 120 post-mortem examinations has been reported for advanced cases. Distant metastasis is unusual but dogs seldom survive more than a year.

Carcinoids of the intestine, liver and gall bladder are malignant but slow growing. Intestinal tumours in dogs invade the gut wall and metastasise, especially to liver. In cats, the inside of the body cavity and lymph nodes are common sites of spread, often with adhesions (where affected tissue sticks to healthy tissue ). In people, removal of tumours, even in the presence of metastases in the liver, may prolong life. In animals, tumours in the abdomen take months to recur but those that appear as metastases in subcutaneous sites, progress rapidly in weeks.

Lung neuroendocrine carcinomas spread within the lung and to more distant organs in approximately a quarter of cases. Surgical removal of part of the lung of dogs can give remission in about three quarters of cases of all lung tumours but average survival times of only 28 days post-surgery is seen in the other quarter of cases. In cats, more tumours are classified as inoperable either because of extensive disease, metastasis or concurrent heart disease. Feline tumours frequently metastasise to bones, particularly those of the toes.

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.