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Neuroendocrine Tumors (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". Your veterinarian may suggest certain tests to help confirm or eliminate 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 about tumors and their treatment in animals is improving all the time.

We understand that this can be a very worrying time. If you have any questions please do not hesitate to ask us.


What are neuroendocrine cells?

Neuroendocrine cells produce specialized chemical substances called "neuroendocrine hormones". These hormones affect the rates of specific chemical reactions in nearby cells or in other tissues throughout the body. Neuroendocrine hormones interact with the nervous system and other types of hormones to integrate and co-ordinate a wide variety of activities that maintain internal stability of the body.

"Neuroendocrine hormones... integrate and co-ordinate a wide variety of activities that maintain internal stability of the body."

Concentrations of neuroendocrine hormone producing cells are present in chemoreceptors (aortic and carotid bodies), the adrenal medulla (the inner portion of the adrenal gland) and the islet cells of the pancreas. They are also scattered throughout the body in a variety of organs including the skin, mouth, esophagus, intestine, liver and lung.


What are neuroendocrine tumors?neuroendocrine_tumors_carcinoids-1

The scattered neuroendocrine cells produce rare tumors (carcinoidsMerkel cell tumors and neuroendocrine tumors). Merkel cells are present in epithelial (outer covering or lining) tissues. Tumors of these cells have been confirmed in the mouths of animals. Neuroendocrine tumors 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 tumors of the aortic or carotid bodies are called chemodectomas (see separate handout). In general, neuroendocrine tumors are slow growing but will eventually spread (metastasize) 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 the culmination of a series of circumstances that 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 neuroendocrine tumors. 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 tumor progression. Some cancers never progress past the first stages so remain benign. Others progress rapidly.


Why has my pet 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 more common in older animals, whose cells have undergone many divisions, or in cells that divide frequently.


Are neuroendocrine tumors common?

These are all rare tumors, primarily recognized in dogs and very infrequent in cats.

"Confirmation of the diagnosis requires specialized and expensive microscopic techniques."

They may be more common than we realize, however, because confirmation of the diagnosis requires specialized and expensive microscopic techniques, sometimes even electron microscopy. Some types recognised in people have not yet been identified in domestic animals.


How will these cancers affect my pet?

Most neuroendocrine tumors do not produce hormones, so clinical problems are primarily associated with their size, which causes compression of the adjacent tissues. In these cases, clinical signs relate to the organ affected.

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


How are these cancers diagnosed?neuroendocrine_tumors_carcinoids-2

Since these tumors do not produce hormones, any clinical signs of these tumors relate to the organ affected. Your veterinarian may suspect the presence of a tumor based on these clinical signs. Further specialized diagnostic techniques may include X-rays, ultrasonography, CT (computerized tomography) scans and MRI (magnetic resonance imaging). These can often indicate the likely presence of a tumor but definitive diagnosis of the type relies on microscopic examination of tissue (histopathology). There is a high probability that routine histopathology, done at a specialized laboratory by a veterinary pathologist, will provide a diagnosis and prognosis (prediction of behavior). Confirmation of the diagnosis may require electron microscopy or expensive and specialized staining procedures such as immunocytochemistry, to eliminate other tumors. These are expensive techniques and not routinely available.

"There is a high probability that routine histopathology, done at a specialized laboratory by a veterinary pathologist, will provide a diagnosis and prognosis."

The sample submitted for examination may be a small part of the mass (biopsy) or the whole lump; if the entire lump is submitted, the pathologist may be able to assess whether the cancer has been fully removed. 


What types of treatment are available?

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


Can these cancers disappear without treatment?

It is not common, but the loss of blood supply to a cancer can make the cells die. Unfortunately, the disappearance of the cancer is rarely complete.


How can I nurse my pet?

After surgery, you will need to prevent your pet from interfering with the incision site and your pet may need to wear an "Elizabethan collar". The surgical site must be kept clean and dry. Report any loss of stitches or significant swelling or bleeding to your veterinarian. If you require additional advice on post-surgical care, please ask.


How will I know how the cancer will behave?

"The histopathology report will give your veterinarian the diagnosis that helps to indicate how the tumor is likely to behave."

The histopathology report will give your veterinarian the diagnosis that helps to indicate how the tumor 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?

'Cured' has to be a guarded term when dealing with any cancer.

Most neuroendocrine tumors 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 tumors in dogs have invaded the gut wall and metastasized, especially to liver. In cats, the inside of the body cavity and lymph nodes are common sites of spread, often with adhesions. In people, removal of tumors, even in the presence of metastases in the liver, may prolong life. In animals, tumors in the abdomen take months to recur but those that appear as metastases in subcutaneous sites, progress rapidly in weeks. 

"Feline neuroendocrine tumors frequently metastasize to bones, particularly those of the toes."

neuroendocrine_tumors_carcinoids-3Lung neuroendocrine carcinomas spread within the lung and metastasize 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 tumors, but average survival times of only 28 days post-surgery is seen in the other 25% of cases. In cats, more tumors are classified as inoperable, either because of extensive disease, metastasis or concurrent heart disease. Feline neuroendocrine tumors frequently metastasize to bones, particularly those of the toes.


Are there any risks to my family or other pets?

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

This client information sheet is based on material written by: Joan Rest, BVSc, PhD, MRCPath, MRCVS

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