What is Carcinoid Cancer?
Carcinoid tumors are a type of neuroendocrine tumor. This type of cancer is rare in cats and is most often found in older cats that greater than seven years of age.
Carcinoid cancer develops due to malignant cell overgrowth of the enterochromaffin cells. Enterochromaffin cells are found in the mucosal linings of the pancreatic ducts, the respiratory tract, biliary tract, intestines, and stomach. Carcinoid tumors are slow-growing, small in size and are marked by their specific location and ability to secrete amines and various peptides. These amines include serotonin, a neurotransmitter that is responsible for sleep and memory, and histamine, a neurotransmitter that plays a role in the immune system.
Symptoms of Carcinoid Cancer in Cats
Because carcinoid tumors produce amines and peptides rather than hormones, symptoms of carcinoid cancer occur in the affected organs due to the compression of the tumor on the organ.
- Loss of appetite
- Weight loss
- Inability to pass stool
- Difficulty breathing
- Pain in the legs due to a blood clot
Causes of Carcinoid Cancer in Cats
The exact cause of carcinoid cancer is unknown. The older a cat is, the more divisions its enterochromaffin cells undergo. A large number of divisions increase the probability of a mutation occurring in these cells, which causes the tumor to form. No specific breeds or prior conditions have been found to increase a cat's risk of carcinoid cancer.
Diagnosis of Carcinoid Cancer in Cats
There are several different ways to diagnose carcinoid cancer in cats. The specific way that the veterinarian selects will depend on the organ that is displaying symptoms. It's important to note all of the symptoms that the cat is experiencing as the symptoms can help the veterinarian determine which organs are being affected.
The veterinarian will order several labs, which will include a complete blood count, a urinalysis and a biochemical blood profile. These tests can help the veterinarian determine which organs are being affected and will show some evidence of a carcinoid tumor, such as mild anemia, elevated liver enzymes and electrolyte abnormalities. Because carcinoid cancer can metastasize to other organs, such as the kidneys or liver, these tests may also show abnormalities in these organs.
Ultrasounds, x-rays, a computerized tomography (CT) scan and magnetic resonance imaging (MRI) may also be done. These tests can help the veterinarian see any tumors that are growing in the cat's body. The presence of a tumor in the digestive, biliary or respiratory tract will require the veterinarian to do a biopsy in order to make a definitive diagnosis of a carcinoid tumor. During a biopsy, the veterinarian will take a small sample of the tumor. The sample will be sent to an outside laboratory for testing. If any of the tests are inconclusive, the veterinarian may order specialized testing, such as staining procedures or electron microscopy, to diagnose carcinoid cancer. These tests will look for substances that are typically excreted by carcinoid tumors.
Treatment of Carcinoid Cancer in Cats
Surgical removal of the tumor is the only known way to stop the tumor from growing, curing the condition. The cat will be placed under general anesthesia during the surgery. The tumor will be removed from the organ lining and the organ will be closed with absorbable sutures. If the tumor has grown to a point that removing it will negatively affect the organ, only a portion of the tumor will be removed.
Radiotherapy, or radiation therapy, may be used in order to reduce the size of the tumor. During this procedure, high-energy waves or particles will be directed toward the tumor, killing the cells and slowing its growth. This treatment carries a high risk of harming the organ or the cells of the organ and is only used when the tumor cannot be surgically removed.
If the tumor has metastasized to the surrounding organs and is untreatable, painkillers will be prescribed for the cat in order to make him or her comfortable during the remainder of its life. If the cat is unable to pass stool due to tumor growth in the intestinal tract, stool softeners may be prescribed in order to help the cat defecate.
Recovery of Carcinoid Cancer in Cats
Cats with carcinoid cancer have a good prognosis if the entire tumor was removed during surgery. Cats who had part of the tumor removed will need to follow up with the veterinarian regularly in order to monitor tumor growth via ultrasounds and lab tests. Tumors that metastasize to the kidneys or liver will need to receive chemotherapy or additional surgery in order to not compromise the function of these organs.
After surgery, it's important to keep the incision site clean and watch for any signs of infection. The cat will need to wear an Elizabethan collar to prevent it from licking or itching its incision site. Follow all of the instructions from the veterinarian following surgery for medication dosage and follow-up care.