Tumors in Ferrets

By Gregory Rich, DVM; Laurie Hess, DVM; Rick Axelson, DVM

Ferrets can suffer from tumors (cancerous growths) in any part of their body, ranging from benign cancers of the skin to aggressive malignant tumors of internal organs. Many ferrets are affected by tumors of the lymphatic system, adrenal glands and the pancreas. See the handouts “Hormonal Diseases in Ferrets” and “Skin Diseases in Ferrets” for more information about adrenal gland tumors and skin tumors.

What are lymphomas?

Lymphomas are tumors of the immune (lymphoid) system and can affect ferrets of all ages, though they appear most commonly in ferrets two to nine years old. Malignant lymphoma (lymphosarcoma) can affect most organs, including the liver, spleen, respiratory system, gastrointestinal tract, eyes, skin, nervous system, heart, kidneys, lymph nodes and the bone marrow. When it affects the bone marrow, it is called leukemia.

The clinical signs of lymphoma depend on the type of tumor, organ involved, and the stage of the disease. Ferrets may not show symptoms for years. Younger ferrets typically develop large tumors in the chest that can spread into the bloodstream. These ferrets become ill very quickly. Older ferrets more commonly develop tumors in internal organs, such as the liver, spleen, and intestines, and can go weeks to months without showing signs of illness.

How is lymphoma diagnosed?

Diagnosing lymphoma can be difficult, as a ferret may display a variety of signs, including lack of appetite (anorexia), lethargy, weight loss, weakness, vomiting, diarrhea, blood in the feces, abdominal distention, bulges or visible masses under the skin, problems breathing, coughing, and hind limb weakness.

In adult ferrets, enlargement of lymph nodes is an important sign, as is enlargement of the spleen, although “Idiopathic Splenomegaly”, a benign enlargement of the spleen, can occur in healthy ferrets.

Your veterinarian may be able to feel masses, and they may take a blood sample for initial testing. A blood sample with a high number of lymphocytes (a type of white blood cell), especially with characteristics of malignancy, may cause suspicion. Your veterinarian may then suggest a bone marrow biopsy to confirm a diagnosis of lymphoma.

Your veterinarian may recommend fine needle aspiration (FNA) or biopsy of an enlarged lymph node or suspected tumor. FNA involves taking a small needle with a syringe and suctioning a sample of cells directly from the tumor and placing them on a microscope slide. A veterinary pathologist then examines the slide under a microscope.

Abdominal ultrasound may be required to identify nodules in the liver, intestines, or spleen. In an organ, surgical biopsy is often required to confirm the cause of the swelling.

What is the treatment for lymphoma?

For a dedicated owner with a compliant patient, surgery and/or treatment with chemotherapy is an option. Adjunctive or supportive treatment with syringe feeding, antioxidants, and immune-stimulating supplements may improve the outcome.

With treatment, lymphoma can go into remission for months to years in ferrets; however, recurrence is common and a complete cure is uncommon. Unlike chemotherapy in humans, chemotherapy in ferrets will not cause nausea or hair loss. The side effects are limited to the blood cells in the bone marrow.

What are insulinomas?

Insulinomas are common tumors of the pancreas that affect insulin production. These tumors may be insulin-producing adenomas (benign) or insulin-producing adenocarcinomas (malignant). Both benign and malignant insulinomas produce excess insulin and may spread (metastasize) to other organs, including the liver. The average age for a ferret to develop an insulinoma is three to five years, but it may be seen as early as two years of age.

Insulin is produced by beta cells in the pancreas and reduces blood sugar (glucose) in the bloodstream. An insulinoma increases the production of insulin, resulting in dangerously low levels of glucose in the blood. The brain relies on glucose to function, so low glucose levels affect the nervous system.

Clinical signs of low blood sugar (hypoglycemia) include: pawing at the mouth, “stargazing” (staring off into space), weakness (often in the hind end), tremors, collapse, abnormal behavior, weight loss, depression, lethargy, and confusion. The symptoms can progress to include seizures, coma, and death.

The adrenal gland may react to sudden reductions in blood glucose by producing adrenaline. Increased levels of adrenaline cause a rapid heart rate, tremors, and irritability. On the other hand, some ferrets with tumors of the pancreas show no early clinical signs or may show only intermittent signs. A ferret that has only intermittent episodes of hypoglycemia may go undetected because the owner may not always witness these symptoms.

How is an insulinoma diagnosed?

Your veterinarian may make a tentative diagnosis based on clinical signs from the physical examination or blood testing. A ratio of insulin to glucose in the blood, despite a low glucose level, can be used to definitively diagnose an insulinoma.

How is insulinoma treated?

Treatment of insulinoma will involve medical and/or surgical therapy, depending on the severity of the disease and on the age of the ferret. The most recent studies have shown that surgery may not dramatically extend survival time when used in conjunction with medical treatment. Depending on the age and health status of the ferret, many veterinarians may recommend both medical therapy and surgery.

Medical therapy involves using a corticosteroid, like prednisone, to increase glucose production by the liver and/or an insulin blocking drug, such as diazoxide, to increase blood glucose levels. These medicines do not stop the progression of the tumor, but will minimize the clinical signs by keeping blood sugar from declining. Ferrets treated with medication must be monitored carefully, as their tumors will continue to grow and their medication dosages typically must be increased accordingly.

Surgery involves removing any visible pancreatic tumor nodules. While it may be possible for an experienced veterinarian to remove visible insulinoma nodules in the pancreas, microscopic parts of the tumor often remain in other parts of the pancreas and liver, so surgery is not always curative and disease recurrence is common.

Diet must also be managed. Ferrets tend to be “grazers” or nibblers when they eat, so it is best to provide numerous small meals daily to provide a more consistent food intake, which also helps level out blood glucose levels. Sugary foods, such as fruit and treats containing molasses, must be avoided, as they cause rapid swings in blood sugar and accompanying surges in insulin. Most veterinarians recommend ferrets with insulinoma eat a high-protein, moderate-fat, low-carbohydrate, commercially available ferret food.

If a ferret collapses or experiences a hypoglycemic coma, emergency treatment is critical for its survival. At home, owners should immediately rub honey, karo syrup, maple syrup, or corn syrup onto the ferret’s gums. If the ferret is experiencing a seizure, be careful to avoid being bitten. The ferret will absorb a small amount of sugar through the gums to help stop the seizure. Then, rush your ferret to the veterinarian, who will administer an intravenous sugar solution and anti-seizure drugs to treat the other symptoms of hypoglycemia. As soon as the ferret is awake and stable, your veterinarian will give it oral medication to raise its blood sugar. A ferret undergoing continuous seizures from hypoglycemia will likely suffer brain damage and death if not treated.

What is the prognosis?

In the largest reported series of cases to date, surgical removal of insulinoma in ferrets demonstrated a mean survival time after surgery of around 500 days, which is relatively long, given that affected ferrets are generally middle-aged.

However, studies have shown that ferrets with insulinoma also respond well to medical treatment with blood glucose-raising drugs. Since many ferrets already have metastasis of the tumor to the liver at the time they are diagnosed, many veterinarians immediately proceed with medical therapy rather than offer surgery as a potential to extend the life of the patient by several more months. Most ferrets respond well to medical therapy and, depending on the severity of the disease, they can live for several months, up to several years.

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