Part III. Avian Cancer Etiologies and Diagnostic Protocols

Some birds, like humans, develop cancer cells during their lifetimes. In most cases, these cells remain dormant and no malignancy occurs. In others, however, the cells multiply, push past the body’s natural immune system, and become abnormal cells. They ignore signals that they are overfilling the space. For nourishment, they create new blood vessels to supply them instead of supplying healthy tissue. They can grow anywhere in the pet’s body.⁵

Normal cells divide, replicate to a certain point, and then stop, but abnormal cells will keep dividing and forming new cells in an uncontrolled manner. Once they are out of control, they are difficult to stop. The body’s immune system does not recognize them as being damaging cells, so it does not destroy them. According to Cathy Johnson-Delaney, normal cells are programmed to die after a certain time (apoptosis), but cancer cells are not programmed that way; they continue to multiply, crowding out healthy cells and spreading the errors onto the new cells.² Sometimes the body’s immune system will seek out damaged or foreign cells and destroy them before they have a chance to multiply and become cancerous growths.³²

All lumps are not tumors. Some lumps can be abscesses which are caused by infectious organisms such as bacteria. Some swellings that the owner notices on his bird might actually be an enlarged organ that increases in size due to disease. If the bird is a female, an abdominal swelling suspected to be a tumor may in fact be an egg.¹

3.1 Causes of Cancer in Birds

The clinician may be able to determine the cause of cancer, but in many cases, the cause is unknown.³² Environmental factors such as second-hand smoke can cause the DNA cells to mutate. Viral infections can cause malignancies. Papillomas (herpes virus) can become malignant and also predispose the bird to cancer of the pancreas and bile duct. These mutations can be passed on to successive generations.³⁶
 

Factors such as environmental toxins, climate changes, stress, carcinogens in the diet, nutritional deficiencies, lack of exercise, inbreeding, and old age can all contribute to errors in cell replication and weaknesses in the body’s immune system. If the immune system is compromised, aberrant cells will take over.^{2, 35} Most cancers and tumors can be treated if they are diagnosed in time.²⁸

Tumors are caused by errors or mutations in the DNA of cells. Normally, cells stop dividing at a certain point, but abnormal cells just keep replicating. The cells appear to be part of the normal body, so the immune system doesn’t try to destroy them.²

3.2 Most commonly Seen Tumors in Birds

While cancer is more commonly seen in older and excessively bred birds, neoplasms can develop in any avian species at any time. The most common external tumor in pet birds is squamous-cell carcinoma (malignant skin cancer). These typically occur on the skin of the head, on and around the beak, on the eyelids, and around the uropygial (preen) gland. It is most often seen in parakeets, lovebirds, and cockatiels, although any species can be affected. Vitamin A deficiency and skin injuries are the primary causes of unhealthy skin. Self-mutilation may also cause the cells to become cancerous. “When a bird chews up its skin and mutilates an area over and over again, the cells can start losing their way and become cancerous,” according to Larry Nemetz.²

The most common internal tumor in pet birds is an intra-abdominal mass, which is usually a tumor of either the reproductive organs or kidneys. These could be either malignant or benign. Abdominal masses are most often seen in budgies that are between 5 and 8 years of age. Most of the time, these types of tumors are not detected until the bird is emaciated and acting very sick. The tumor blocks the digestive tract, and food cannot pass through. Also, droppings stick to the vent and cause blockage. Birds may have labored breathing as the tumor causes the air sacs to collapse, and pressure on the nerves of one leg can cause lameness.²

3.3 Determining if the Tumor is Benign or Malignant

According to Richard Nye, some tumors found in birds are benign, and some are malignant. Cancerous tumors invade other tissues surrounding them or will metastasize to other locations in the body.^1,2 Both can be life-threatening to pet birds, but benign growths are generally considered to be less serious than malignant tumors.² However, some benign growths, such as lipomas, fibromas, and xanthomas, can become malignant.²²

3.3.1 Benign tumors

Benign tumors tend to be limited to one area of the body and do not metastasize but should still be evaluated by the practitioner. They grow and increase in size very slowly. They are usually easy to remove and don’t recur. They might not need to be removed if they are not growing or causing difficulty for the bird, but they should still be monitored for signs that they are growing or becoming troublesome for the bird. At that point, they may need to be removed. An internal benign tumor can cause pain in the bird by putting pressure on the organs, Nye states. As it grows, the tumor will affect or change the surrounding organs; for example, a kidney tumor, even a benign one,  can put enough pressure on the sciatic nerves to the leg or foot to make standing painful.²

3.3.2 Malignant tumors

Malignant tumors invade and damage other tissues and organs near them. When they metastasize, the cancer cells break away from the malignant tumor and travel through the bloodstream or the lymphatic system to form new, secondary tumors in other parts of the body. Removal may be difficult and may not stop tumor growth. New tumors may grow quickly in places where the tumor has metastasized.²

Normal tissue cells are of the same size, appear uniform, and are organized in an orderly way.  Cancer cells look less orderly, have haphazard organization, and are of varying size.  Often, cancer cells will divide rapidly (called mitosis), so the pathologist will count them and be able to tell how aggressive the tumor is. The faster the cells grow and divide, the more dangerous the cancer is.³⁶

3.4 Diagnosing Tumors in Birds

Benign and malignant neoplasms may occur anywhere in the bird’s body: on the skin, in the sinuses, oral cavity, GI tract, lungs, air sacs, liver, spleen, kidneys, reproductive tract, bone, vascular and connective tissue, and brain. External tumors may be found on physical examination and diagnosed by fine-needle aspirate, cytology, and/or biopsy (taking a tissue sample). Internal growths require imaging such as radiographs, ultrasound, or CT scan, endoscopic examination, or exploratory surgery to determine the type and extent of the neoplasia. ¹⁴

3.4.1 Physical exam and history

The veterinarian will diagnose based on the bird’s history, examination of the mass and its progression, a full-body physical examination,  radiograph results to view malignancies, and blood-test results. The pathology result will determine if the tumor is cancerous.³⁶ “This information is important since many tumors tend to affect birds of a certain species, age, and gender.”¹¹ If he discovers the bird is malnourished and has chronic hypovitaminosis A,  he can look for signs of squamous cell carcinoma. The bird’s reproductive history will indicate if a chronic egg-layer is at risk for ovarian or other reproductive cancers.¹¹

3.4.2 Biopsy

Without tests, the veterinarian will not be able to tell if the lump is cancerous. The examination is important, but he needs to perform tests to confirm his diagnosis. A fine-needle biopsy can often diagnose the composition or cause of the lump. Sometimes he will take a biopsy and send it out for histological testing (examination of the tissue microscopically) after surgical removal in order to determine if the tumor is benign or malignant. “Internal lumps may require other diagnostic tests, including blood tests, radiographs (X-rays), ultrasound, or even exploratory surgery in order to determine their nature.” ¹

A biopsy is needed to determine if the tumor is benign or malignant. Cells are removed for microscopic examination by using a fine-needle aspirate (inserting a small needle into the mass and extracting cells) or by excising a small piece of the growth or the entire growth for examination.³⁶ “Biopsies or aspirates should be taken where normal tissue and abnormal tissue meet and should include inflamed or ulcerated tissue. Bone biopsies should be taken at the center of the lesion.”¹¹ The clinician may take an impression smear; to do this he will press a clean slide onto the mass for staining and examination. This is often used if the mass is ulcerated. These cells are then studied by a pathologist.³⁶

3.4.2.1 Skin biopsy

Skin lesions are quite common in birds. They range from feather picking to Psittacine Beak and Feather Disease (PBFD) and tumors. Many birds have infections in their skin from fungi, bacteria, viruses, or parasites. To treat it, the practitioner needs to find the etiology behind a skin disease. There are several tests that can be used, such as skin scraping, impression testing, and biopsy.  “Skin biopsies are a viable diagnostic tool in dermatology and they are also taken in birds. Due to the very thin avian skin, their biopsies have the tendency to roll or contract, both leading to severe difficulties to separate artifacts (things that are not naturally present but occurs as a result of the investigative procedure) from real pathological items. The biopsy technique using a tape strip is quick, inexpensive, and gives good results. In this technique, non-translucent, self-adhesive tape (Scotch tape®) is attached to skin biopsy sites before obtaining skin biopsies using a standard skin biopsy punch instrument.” For information on this technique, go to: http://www.vetcontact.com/dermatology/art.php?a=21changes

3.4.3 CBC

A CBC (Complete Blood Count) and chemistry panel may be performed with a blood test, and radiographs will be run “to evaluate the bird’s overall health status and identify any underlying disease.” ¹¹ Older females, especially Amazons and cockatiels, are prone to cardiovascular disease, particularly atherosclerosis, and these tests will help determine the treatment and prognosis. The bird may suffer from renal or hepatic enzyme elevation, indicating organ involvement. If the bird is anemic or has leukopenia (low white blood cell count), bone marrow or splenic disease may be present. This information is necessary when determining treatment, particularly the use of immunosuppressive drugs.¹¹

3.4.4 Cytology and immunohistochemistry

If the clinician suspects a tumor, he will run histologic and cytologic tests to help with diagnosis. From those, he can determine the type of tumor and its condition. Cytology will tell if the tumor is malignant or benign. Immunohistochemistry will “determine various cellular antigens and cells of origin. Mitotic index can help determine tumor grade.” (Tumor grade is the description of a tumor based on how abnormal the tumor cells and the tumor tissues look under a microscope. It is an indicator of how quickly a tumor is likely to grow and spread. The mitotic index tells how quickly abnormal cells are dividing.)¹²
 

3.4.5 Imaging

In order to diagnose the tumor, the clinician may use conventional radiography, magnification radiography, contrast radiography, ultrasonography, fluoroscopy, magnetic resonance imaging (MRI), computed tomography (CT), and bone scans. These are some of the imaging modalities that are useful in exotic oncology cases. These modalities will provide the location of the tumor in the body and tell the size and extent of the tumor and how far it has metastasized. Limitations of MRI and CT include difficulty of acquiring useful images due to small patient size, difficulty of providing anesthesia, expense, and limited availability of equipment in some areas.¹² (However, recently there has come on the market a new CT scanner called the “Micro-CT scanner").
 

According to Larry Nemetz, some owners wait too long to have the mass diagnosed, thinking it will go away with time; meanwhile, the mass grows quite large. The sooner the mass is attended to, the greater the success rate of the treatment. If the owner waits, the tumor will metastasize, and often it is too late to save the bird.²

If a neoplasm is detected, it is usually best to remove it surgically. This may be difficult depending on the size and location, so it’s important that the tumor be seen early in its development. If it cannot be removed, it may be possible to debulk it and reduce it in size in order to improve the bird’s quality of life.¹

By examining the bird regularly, the owner will be able to find any growths present.  Any external growth should be seen by the avian veterinarian who will decide if the growth should be subjected to biopsy. Observe if the bird is standing differently than usual, holding one foot up, has changed in eating and sleeping habits, or is losing weight. It may be a tumor or some other condition. Malignant internal tumors do not usually have a good prognosis. “Internal benign tumors can also put pressure on the bird’s organs, which can be painful or uncomfortable. A tumor takes up space, and wherever it is in the body, if it continues to grow, it’s going to displace or change what’s going on with the surrounding organs,” David Phalen states.²  

3.5  Primary and Secondary Tumors

A primary tumor is a tumor as it first appears in the original site. Tumors that spread and metastasize to other areas of the body are secondary tumors.

3.5.1  Primary tumors (T)

A primary tumor is diagnosed through aspirates for cytology and biopsy for histologic testing. If the tumor is localized, complete surgical excision of the mass may affect a cure. The clinician may be able to tell how the tumor has spread through clinical examination, but usually, the disease goes beyond the margins of the tumor, so testing is needed. The site of the tumor determines the tests used.¹²

3.5.2 Secondary tumors or metastatic disease (M)

Tumors may metastasize to any organ or site: the skin, liver, kidneys, bone, brain/nervous tissue, and spleen. Lungs are a common site. Techniques for localizing and evaluating metastases are:

• "Multiple radiographic views to show changes in the size or shape of the liver, spleen, and kidneys
• CT or Micro-CT scan for more sensitive evaluation.
• Ultrasound-guided aspirates or endoscopic biopsies to determine the extent of disease in these organs.
• Bone-marrow aspiration for staging and diagnosing disseminated diseases like lymphoma or leukemia.
• Positron emission tomography (PET) scan and technetium-99 bone scan."¹²

3.6 Internal and External Malignancies

M. Wissman states that birds can develop the same types of cancer as humans and other animals do. The most common external tumors are skin tumors and squamous cell carcinomas. The most common internal malignancies are those of the kidneys or reproductive organs.³⁶

Internal cancers are difficult to diagnose. Tumors can be found in kidneys, liver, stomach, glands (ovary, testicle, thyroid, and pituitary), muscles, or bones. When diagnosed early, most internal tumors can be treated with surgery to prolong or save the bird’s life. However, if the cancer is located in a difficult place, surgery will not be an option.²⁸ (In past years, radiation and chemotherapy were used, but they are not used anymore. The success rates were poor and the birds died in spite of treatment. R. Dahlhausen, personal communication).

3.7 Cancer and the Geriatric Bird

Birds can develop tumors at any age, but they tend to be more common in older birds.¹ Because aging changes the cellular structure in birds’ bodies, older birds have higher cancer rates. Diet, climate changes, and stress contribute to those changes.³⁵ Ovarian neoplasias, renal carcinomas, hepatic adenocarcinoma, hepatobiliary and pancreatic adenocarcinoma, splenic, esophageal, and gastric carcinomas have all been reported in older psittacines.¹⁸