Conditions Due to Abnormal Secretions from a Tumor in Dogs

Tumors can cause a variety of problems throughout the body, some related to their direct physical presence and others due to an indirect effect on metabolism and other functions. Any disorders not directly related to a tumor or to cancerous metastasis are referred to collectively as paraneoplastic syndrome (PNS). PNS is usually caused by tumors that secrete hormones, peptides and other proteins. Secretions may come from the tumor itself, or from other cells reacting to the tumor. These hormonal secretions aren’t controlled by the body’s normal regulating system, so they can cause serious metabolic imbalances. Most tumors that cause PNS are malignant, but occasionally benign tumors may produce secretions also. Generalized problems include weight loss despite normal food intake (especially loss of muscle tissue), weakness, and sometimes fever. Symptoms related to a specific secretion can cause secondary conditions like hypercalcemia (most common in dogs) or hyperadrenocorticism (some types of Cushing’s disease are related to PNS). In many cases, PNS may be the first sign your dog has cancer, so it can be a very important diagnosis.

Cancerous tumors often secrete hormones and abnormal proteins that can affect your dog’s metabolism and cause a number of different problems. This condition is paraneoplastic syndrome. It may be one of the first signs your dog has cancer.

Symptoms can be quite varied, depending on the location and type of tumor involved. Any of these signs should be evaluated by a veterinarian.

• Weight loss
• Weakness
• Lethargy
• Fever
• Constipation
• Diarrhea
• Excessive drinking
• Frequent urination
• Lameness
• Neurological symptoms (seizures)
• Alopecia (hair loss)

Types

Many different conditions could be related to PNS. These are some of the most common types in dogs.

• Cachexia, which is weight loss, especially loss of muscle, without caloric reduction
• Fever, caused by tumors that produce pyrogens
• Hypercalcemia of which cancer is the main cause in dogs, commonly related to parathyroid tumors, lymphoma, adenocarcinoma (especially of the anal sac), and multiple myeloma
• Hyperadrenocorticism (Cushing’s disease)from tumors in the pituitary or adrenaline gland, and rarely tumors in the lungs or abdomen
• Hypoglycemia results due to insulinoma in the pancreas and sometimes the liver
• Hypergastrinemia resulting from non-cutaneous mast cell tumors (mastocytosis) which cause vomiting and abdominal pain (Zollinger-Ellison syndrome)
• Blood cell abnormalities like anemia, abnormal white blood cells counts, and hyperviscosity syndrome can all be related to cancer
• Hypertrophic osteopathy is abnormal bone growth that can cause lameness in one or more limbs with a variety of different tumors
• Cutaneous symptoms such as glucagonoma of the pancreas can produce skin lesion; tumors of the testes or uterus can also cause hormone imbalance that results hair loss

Most types of cancer are idiopathic. Inherited tendency, diet, and environmental factors may be related, but these factors haven’t been well enough studied in dogs to make a connection. Cancer is more common in older dogs, so PNS-type syndromes in a younger dog would be more likely related to another problem.

Many types of PNS, including hypercalcemia, hypoglycemia, hyperadrenocorticism, and abnormal blood cell counts, are evident on a blood test. This can sometimes be diagnosed on a routine check-up if your dog is not showing symptoms. Otherwise the veterinarian will analyze your dog’s symptoms. 

Further tests will be ordered, depending on the type of cancer that is suspected. X-rays, ultrasound, CT scans or MRI’s can help diagnose tumors. Exploratory surgery, biopsies, and other tests may be needed to find the source of the problem. Other tests will rule out non-cancerous causes of PNS-type syndromes.

The veterinarian will need your dog’s family and medical history, as well as any recent and current medications. Diagnosing cancer can sometimes be a long process, so several appointments and some potentially invasive tests may be necessary.

Treatment for PNS will focus on stabilizing the immediate symptoms as well as eliminating the cancer that is the source of the problem. Some life threatening metabolic imbalances (like severe hypercalcemia or hypoglycemia) can occur with PNS. Seriously ill dogs will need immediate treatment with fluids and electrolytes to balance the problem. Other medications will be given to avoid recurrence of a crisis. With tumors that are inoperable (like many pituitary tumors that cause Cushing’s disease) this could be a lifelong medication. High-fat diets and nutritional supplements may be recommended for weight loss related to cancer.

The second focus of treatment involves eliminating the cancer. Surgery is the best option for tumors, but this may not be possible depending on the placement of the tumor and your dog’s overall health. Chemotherapy or radiation may be prescribed in addition to or instead of surgery. These treatments can have significant side-effects, so it’s important to discuss the effectiveness of any treatment with your veterinarian. If the cancer is not treatable, medication will focus on reducing the symptoms of PNS as long as possible. In some cases the veterinarian may recommend euthanasia.

Most cancer diagnoses have a guarded prognosis. Tumors that are found early and removed with surgery may remain in remission for a number of years. Others may return in only a few months. Some forms of slow-developing cancer are manageable symptomatically for an extended period of time. Early treatment is the best option, so it’s a good idea to have regular check-ups as your dog ages and follow up on any problems. Catching PNS early will give your dog the best chance of survival.