Avian Cancer

Your bird has developed a lump on the wing, and you schedule an appointment with your avian veterinarian for evaluation of this suspicious mass. Testing uncovers a malignant tumor: cancer. This is the diagnosis that anyone dreads hearing, whether for themselves, a loved one or a beloved pet.

What is cancer? Cancer is a type of neoplasia, which is an abnormal, uncontrolled, progressive growth of cells in any tissue or organ. Neoplasms are classified based upon the general tissue origin, specific cell line type and whether or not the neoplasm is benign (words usually ending in -oma) or malignant (sarcoma or carcinoma). It is group of malignant tumors that are considered cancerous.

Cancer is caused by damage (mutations) to the DNA. DNA is like a set of instructions for cells, instructing them how to grow and divide properly. When a mutation occurs in the DNA, normal cells will repair the mutation or simply die off. Sometimes, the cells continue living with the mutation, and as a result, they grow and divide in a chaotic fashion. One malignant cell becomes two, two become four, four become eight, and so on, until a mass of cells (a tumor) is formed. Tumors eventually interfere with normal body functions and sometimes spread to other parts of the body.

Mutations in DNA can be caused by environmental factors, such as bird inhaling second-hand smoke (although this has not been proven in birds at this time). In some cases, it can be possible for mutations to be passed on from one generation to the next. In birds, certain viral infections have been associated with malignancies. For example, birds suffering from papillomas, caused by a suspected herpes virus, seem predisposed to certain malignancies, such as cancer of the pancreas and bile duct, and the papillomas themselves may become malignant.

Not all tumors are cancerous, and not all cancers form tumors. For example, leukemia doesn't form one single mass, but causes abnormal cells in the blood, bone marrow, the lymphatic system and spleen.

What does cancer look like? Unfortunately, it is impossible to tell if a tumor is malignant or benign just by looking at it or palpating (feeling) it. The only sure way is to perform a biopsy, a technique whereby some cells are removed for microscopic examination. This can be done with a fine needle aspirate, where a small needle is inserted into the mass and cells are extracted for staining and examination under the microscope. Sometimes, excisional biopsies are performed, where all of the mass is surgically removed, then portions are examined microscopically. Another method is called an impression smear, which can also sometimes be used for attempting to diagnose malignancies. If the mass is ulcerated, a clean slide can be pressed into the mass for staining and examination.

Other tests can lead an avian veterinarian to a presumptive diagnosis. The history, or the owner's interpretation of the progression of the mass, is very important. Thorough physical examination of the entire bird is very important. Radiographs (x-rays) can show classic lesions that give the appearance of a malignancy. Certain blood tests can also help in the diagnosis. But, the only way to know for certain if a mass is cancerous is to have a pathologist examine the suspicious tissue under the microscope.

How does a pathologist tell malignant cells from benign ones? Normal tissue usually has cells that appear uniform, with similar size and orderly organization. Cancer cells look less orderly, often have haphazard organization and have cells of varying size. Often, cancer cells are rapidly dividing (this is called mitosis) and often counting the number of mitotic figures (present during cell division) helps the pathologist determine how aggressive the tumor is, as the faster they grow and divide, the more dangerous the cancer is (as a rule).

What kinds of cancers do pet birds get? Many types of tumors have been diagnosed in pet birds, including tumors of the skin and internal organs. Budgerigars seem to be one species of bird that is very prone to cancer. Probably the most common malignancy diagnosed is an internal tumor of either the kidney or gonad (ovary or testicle). As the tumor grows, often the first sign of trouble is lameness of one leg. This occurs because the tumor often impinges on the nerves to the leg on that side, resulting in lameness. Eventually, the abdomen may become distended, either because the tumor continues growing, or because fluid accumulates in the abdomen. Some tumors of the testicle or ovary produce hormones opposite of the sex of the bird, so a male budgie may develop a brown cere (the normal adult color of most male budgies is blue), or a female budgie that normally has a brown cere may suddenly develop a blue cere.

A male budgie patient of mine (with a beautiful, deep blue cere), named Fax, developed a testicular tumor that produced female hormones. His cere went from blue to tan in a short period of time. My client did not want to put him through a major surgery, and he went on to live for another year and a half before succumbing to his cancer.

Ovarian carcinoma and adenocarcinoma are types of cancer that can be very dangerous, as surgical removal of the entire mass is difficult, if not impossible, as the ovary is closely associated with large blood vessels. For this reason, the cancer may reoccur after surgical removal. Clinical signs may include abdominal distension, fluid build-up in the abdomen, breathing problems, weakness or paralysis of the left leg and a visible or palpable mass in the abdomen. Hens may also develop cancer of the oviduct. If caught in time, it might be possible to remove the oviduct with the malignancy, however, these tumors often metastasize to the surfaces of other internal organs. Just about the worst tumor that I have ever seen was one that developed in the oviduct of a Hyacinth macaw that actually eroded through the body wall and bulged out in the area of the hip on the left side. By this time, the tumor was inoperable, unfortunately.

Tumors involving the kidney may cause signs of increased urination and concomitant increased thirst and advanced tumors may result in gout formation.

Unfortunately, these types of tumors are often not detected until the mass has grown to a size making surgery risky. Some tumors will have invaded surrounding tissues and organs, making complete excision impossible and other tumors may have already traveled to other organs, called metastasis, which means that the bird will not be cured.

When dealing with tumors, in some cases, complete surgical removal is curative. However, there is always a concern that a tumor might have already spread to other organs, so additional tests might be necessary, including radiographs (x-rays), MRIs or CT scans, to ascertain if any suspicious masses are present elsewhere in the body. When dealing with a malignant tumor on a limb, it is often best to amputate the limb to try to prevent problems with cancer reoccurring in the future. While this may seem like a drastic measure, birds adapt very well to the loss of a limb (or partial limb).

With some cancers, in addition to surgical excision of the mass, chemotherapy or radiation therapy may also be warranted. There are some quite sophisticated treatments and procedures that are now available for avian patients with cancer, however these may only be available at referral centers, veterinary colleges and specialty centers.

As with other species, cancer rates increase as avian patients age. Since avian medicine has dramatically improved the quality of life for many birds, and birds are living longer lives, we can expect that we will see more cases of avian cancer in older birds, however it is not unusual to see some types of cancer in budgies and other small birds that are as young as four or five years of age.

Fibrosarcomas (tumors arising from connective tissue) are one of the more common types of cancer found in birds, and these are often seen on the wing or leg. They are most often diagnosed in budgerigars, cockatiels, macaws and other species of parrot. They often feel like a firm mass surrounding a long bone, and if large enough, this type of tumor might result in the skin over it becoming ulcerated from the bird picking at it or because the skin has become compromised. If discovered early on, surgical removal, often involving amputation of the limb, can be curative, however, these are likely to metastasize to lung, liver, bone or elsewhere with time. I have removed many a fibrosarcoma, most often from the wings of cockatiels, and most have gone on to live long, happy lives, albeit, with only one wing remaining!

Many birds that tend to be overweight or downright obese are prone to developing tumors called lipomas or xanthomas. While these tumors are benign (non-malignant), they may grow to be very large, and may interfere with normal movement. Lipomas may occur in multiple areas of the bird's skin. Large masses may result in the skin over them ulcerating from the birds picking at them or from loss of blood supply. Xanthomas are not true tumors, but may occur in multiple locations, acting like benign masses. Rarely, liposarcomas may develop, which have the appearance of lipomas and are usually found in the area of the keel bone or uropygial gland. These cancers have the potential to invade nearby tissues and can also metastasize to other areas of the body.

Skin cancer is not common in pet birds, most likely because they are not exposed to the damaging rays of sunlight, as many outdoor birds are. Squamous cell carcinoma, a common human skin cancer, has been diagnosed in chickens and other free-ranging birds. Fortunately, this is one type of cancer that we won't need to worry about in pet birds, even those with bare facial skin, unless they are exposed to high levels of damaging ultraviolet rays from the sun. Another type of skin mass found in some birds, most commonly African Grey parrots, is the cutaneous papilloma. These are most often located around the eyelid, junction of the beak and face and on the feet and legs. Papillomas are viral-induced in African Greys, and I mention this because internal papillomas (also most-likely viral-induced) can also undergo malignant transformation to become squamous cell carcinoma. These may be found anywhere along the gastrointestinal tract.

Pancreatic adenocarcinoma (cancer of the pancreas) and cholangiosarcoma (cancer of the bile duct) may occur in birds with internal papillomatous disease, which is thought to be associated with a herpes virus. Cancer of the proventriculus occurs more frequently than cancer of the ventriculus. Rarely, cancer involving the intestines occurs. Masses and neoplasms of the cloaca have been diagnosed, and have been seen most frequently in Amazon parrots.

Cancerous lesions can occur in the liver or bile duct. Often, multiple masses may be observed within the liver tissue itself, or a single tumor may be present. Carcinoma of the liver is often difficult to diagnose in the early stages, and by the time the tumor is large enough to be noticed (usually by abdominal swelling), it may be too late to save the bird. Sometimes, there will be a large amount of fluid in the coelom from the damage to the liver. Radiographs, ultrasound, endoscopy, laparoscopy or biopsy may be used in diagnosing some of these tumors. If a tumor is restricted to one lobe of the liver, it may be possible to excise that portion of the liver, however, these tumors may spread to the lungs, so it is always important to confirm that the lung fields look clear prior to attempting surgical removal of a solitary liver tumor.

The uropygial gland may develop a malignant tumor, and these are most often seen in the budgerigar and canary. The gland (which is normally bilobed, heart-shaped and located at the base of the tail on the back) has a wick feather that the bird preens and then applies the secretion to the feathers. Not all parrots possess an uropygial, or preen, gland, however.

Primary lung tumors or cancer in the respiratory system are uncommon in parrots, but the lungs are often the site for metastatic neoplasia. Fibrosarcoma, adenocarcinoma, hemangiosarcoma, malignant melanoma, mesothelioma and osteosarcoma may all travel to the lungs in cases where the primary tumor has spread.

Occasionally, tumors arising from the blood vessels and may be found in the skin, liver, lung, spleen, muscle, mesentery, kidney, heart, oviduct, bone or other tissues. These may occur singly or in groups. These are often very dangerous types of cancer, capable of invading locally or spreading to distant tissues, such as the lung, liver or heart muscle.

Tumors of the muscles, leiomyosarcoma (from smooth muscle) or rhabdomyosarcoma (skeletal muscle in origin) are not common, but occur. Cancer originating from cartilage or bone are occasionally seen. Osteosarcomas are usually a very dangerous type of cancer originating in long bones of the wing or leg, but can also develop on the rib, skull, eye socket, toe or tail bone. This type of tumor may erode through the bone, resulting in a spontaneous fracture of the bone. Amputation of the limb containing an osteosarcoma lesion is usually the best course of action.

Leukemia and lymphosarcoma are two very dangerous types of cancer involving the white blood cells and lymphatic system, respectively. Leukemia can involve either lymphocytes or granulocytes, two cell lines of white blood cells. I have most often seen leukemia in adult macaws. In spite of aggressive chemotherapy in several cases, none of the birds went into remission of the disease. There is a close association between the virus responsible for Marek's disease and certain cancers in chickens and there are suspicions that some leukemias in birds and other species may be associated with some viruses, as well.

With the new chemotherapeutic agents, chemotherapy medications, surgical techniques and concentrated radiation treatments, cancer is not always a death sentence for avian patients. Many more birds are surviving for years after being diagnosed with cancer. If your bird has been diagnosed with a malignant tumor, ask your avian vet if your bird should be referred to a specialist or referral center for appropriate therapy. Aggressive surgery or therapeutics after thorough diagnostic testing will give your pet the best chance for a cure from many types of cancer; however, time is always of the essence. So, if you find a suspicious lump or bump, have your bird examined and evaluated as soon as possible so that appropriate diagnostics and treatment can be instituted. It's the best way to ensure that your bird will live a long and healthy life.


Cadeusus
Copyright 2006 Margaret A. Wissman, D.V.M., D.A.B.V.P.
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