Tumors and Cancers - Healthy Dog Experts

A tumor is any sort of lump, bump, growth or swelling. Tumors that are true cancers are called neoplasms. Tumors can be divided into two broad catagories: benign and malignant. Benign tumors grow slowly, they dont invade or destroy neighboring tissue, and do not spread to other parts of the body. These cancers are usually not life-threatening cancers and are also called carcinomas, sarcomas or lymphomas, depending on the tissue where they originated. Cancers invade neighboring tissue and continue to grow in an unrestricted way. At some point, malignant cells part from the primary tumor and enter the lymphatic system or the circulatory system and establish new colonies in other areas. This process is called metastasizing. Any new growth on your dog should be examined by a professional doggy doctor. The majority of cancers in dogs are detected by physical examination. About half are visible as growths or sores on or beneath the skin. Perianal tumors, testicular tumors, mammary gland tumors, lymph gland tumors and cancers in the mouth can be detected by inspection and palpation. Bones tumors can be recognized by a swollen limb, lameness or the appearance of a swelling that involves the bone. Internal cancers are most common in the spleen, liver and gastointestinal tract. Cancers in these areas often become advanced before they are even suspected. Usually the first signs are weight loss, a palpable mass in the abdomen, vomiting, diarrhea, constipation or gastrointestinal bleeding. Lung cancer is rare in dogs. However, dogs are at risk from secondhand smoke. The lungs are also a frequent site for metastases. The same of the liver. The majority of cancers occur in middle-aged and older dogs. Because companion animals are living longer and enjoying a higher quality of life, it is likely that cancers will be diagnosed with increasing frequency. A routine physical exam will detect most cancers. Regular visits to your local doggy doctor will provide the opportunity to detect cancer at an early stage. This has significant implications for the life and health of your pet. As a rule, healthy dogs 7 years of age and older should have a physical examination at least once a year. If their health is questionable, they should be seen more often. If any signs develop they should be seen at once.

What Causes Cancer?

Cancer is a condition in which rapid cell division and tissue growth occur at the expense of the host organ. Most cells in the body die and are replaced many times during the course of a dog's life. Cell reduplication follows an orderly pattern controlled by the genes. When things go smoothly, each duplicated cell is an exact clone of its ancestor and assumes the same role. Anything that disrupts the genes that govern cell duplication results in the production of mutant cells. Mutant cell often reproduce at an extraordinary rate and form large masses that crowd out normal cells. Such a mass is called a cancer. Further cancerous cells do not function as normal cells and thus do not provide needed services. If the cancer grows unchecked, it eventually replaces much of the organ while also metastasizing to other parts of the body. In time, it causes the death of the dog. Some cancer producing genes are inherent in the breed or genetic makeup of a dog. Bernese Mountain dogs, for example: have a high incidence of cancers affecting all body systems. Approximately one in four Bernese Mountain Dogs will develop cancer. Two of the cancer types seen in this breed are histiocytosis and mastocytoma - are known to be inherent as polygenic traits. A number of genes have been identified causing breast, colon and other cancers in people and in some animals. The reason that all individuals with these genes do not develop cancer is that there are other specific genes that supress the cancer genes. To complicate matters, there are still other genes that inhibit the suppressors. All these genes are turned on and off by external factors, such as diet, stress and environment. Thus, cancer is a largely unpredictable phenomenon involving a complex interaction of genetics and the environment. A good example is bladder cancer in Scottish Terriers. Scotty's have an increased risk of bladder cancer to begin with. If you add in exposure to lawn chemicals that contain 2,4D, the risk increases four to seven times. In this case, genes and an environmental influences known to increase the likelyhood of cancer in direct proportion to the length and intensity of exposure. Carcinogens gain access to tissue cells, cause alterations in genes and chromosomes and disrupt the system of checks and balances that controls orderly growth. Examples are carcinogens known to increase the risk of cancer in humans are ultraviolet rays (which can cause skin cancers), X-rays (thyroid cancers), nuclear radiation (leukemia), various chemicals (aniline dyes cause bladder cancer), cigarettes and coal tars (lung, bladder, skin and many other cancers), viruses (sarcoma in AIDS patients), and internal parasites (bladder cancers). Secondhand smoke exposure is associated with cancer in animals as well as in humans. Injuries are sometimes implicated as causing cancers, but there is a seldom connection. Trauma causes hematomas, bruises and contusions, but does not cause abnormal cell growth. However, an injured site is usually examined closely, and small pre-existing tumors are sometimes discovered this way. Bone cancers may be more likely to develop at the site of previous fractures. Some benign tumors, such as warts and papillomas, are clearly due to a virus. Other benign tumors simply grow for unknown reasons.

Common Surface Tumors

Skin tumors are common in dogs. It is often impossible to determine whether a skin tumor is benign or malignant by appearance alone. The only conclusive way to make a diagnosis is by biopsy, a procedure in which tissue or cells are removed by a trained professional and examined under a microscope by a veterinarian pathologist. For small tumors it is best for your veterinarian to remove the growth and present the entire specimen to the pathologist. For tumors larger than one inch (2.5cm) across, it may be advisable for your veterinarian to obtain a tissue sample by fine needle aspiration. In this procedure, a needle connected to a syringe is inserted into the tumor and cell are obtained by pulling back on the plunger. Alternatively, the vet can use a cutting needle to obtain a core sample. An open biopsy, in which an incision is made, is preferred for suspected sarcomas and tumors that present diagnostic problems for the pathologist. Additional information on the size of the tumor and the extent of local involvement may be important in planning treatment. Ultrasonography, available in many dog clinics, provides diagnostic information that cannot be obtained through conventional X-rays. CT scans and MRI are used to diagnose some internal cancers and determine the extent of local involvement.

Epidermal inclusion cysts, also called sebaceous cysts are common surface tumors found anywhere on the body. Kerry Blue Terriers, Schnauzers, Poodles and spaniels are most often affected. Epidermal inclusion cysts begin when dry secretions block hair follicles, causing an accumulation of hair and sebum (a cheesy material), and the subsequent formation of a cyst. These cysts produce a dome-shaped swelling up to an inch or more in size beneath the skin, though most are smaller. They can become infected and may need to be surgically drained. This sometimes leads to a cure.

A lipoma is a benign growth made up of mature fat cells interlaced with fibrous connective tissue. Lipomas are common in overweight dogs, especially females. A lipoma can be recognized by its oblong or round appearance and smooth, soft, fatlike consistency. Lipomas grow slowly and may get to be several inches in diameter. They are not painful. Rarely, what appears to be a lipoma is a malignant variant called a liposarcoma.

Histiocytomas are rapidly growing tumors found in dogs 1 to 3 years of age. They occur anywhere on the body. These benign tumors are dome-shaped, raised, hairless surface growths that are not painful. Because of their appearance, they are often called button tumors. These benign growths are more common on short-haired dogs.

This is a rare malignant cancer in which histiocytes (large cells found in normal connective tissue) are widely dispersed throughout the subcutaneous tissue and internal organs, occasionally forming nodules. The typical signs are lethargy, weight loss and enlargement of the liver, spleen and lymph nodes. The disease tends to affect male dogs of certain breeds at 3 to 8 years of age. In Bernese Mountain Dogs, the disease is inherited as a polygenic trait and accounts for 25% of all tumors in that breed. Flat-coated Retrievers are also unusually suseptible to this type of cancer.

These are common benign tumors found more often in older dogs, particularly Boston Terriers, Poodles and Cocker Spaniels. The average age of dogs with sebaceous adenomas arise from the oil-producing sebaceous glands in the skin. They tend to occur on the eyelids and limbs. They may be single or multiple, usually are less than one inch across and appear as smooth, lobulated growths on a narrow base or stem. The surface of the tumor is hairless and may be ulcerated. Occasionally, a sebaceous adenoma becomes malignant (becoming a sebaceous adenocarcinoma). Suspect malignancy if the tumor is larger than one inch, has an ulcerated surface, and is growing rapidly.

Mast cell tumors are common, accounting for 10 to 20 percent of skin tumors in dogs. About half of them are malignant. Brachycephalic breeds, such as Boxers, Boston Terriers and Bulldogs have a higher incidence. However, mast cell tumors can occur in all dogs. In Bernese Mountain Dogs, mast cell tumors are especially common and are inherited as a polygenic trait. The age for dogs to develop mast cell tumors is 9 years. Both sexes are equally affected. Multiple tumors are present in 10 percent of cases. Look for these tumors on the skin of the trunk and perineum, lower abdomen, foreskin of the penis and hind legs. Mast cell tumors vary greatly in appearance. The typical tumor is a multinodular growth that appears reddish, hairless and ulcerated. It is impossible to tell by appearance whether the tumor is benign or malignant. Some growths may be present for months or years, then suddenly enlarge and metastasize to the regional lymph nodes, liver or spleen. Others grow rapidly right from the start. Still others may be completely under the skin and look like a lipoma. For that reason, all new lumps should be checked. Mast cell tumors release histamine and other substances that cause stomach and duodenal ulcers. In fact, up to 80 percent of dogs with mast cell tumors may be suffering from ulcers. Dogs with intestinal symptoms should be evaluated for ulcer disease and treated accordingly.

These tumors are induced by exposure to the ultraviolet radiation in sunlight, and occur on lightly pigmented areas of the body, including the underside of the belly, trunk, scrotum, nail beds, nose and lips. One variety of squamous carcinoma appears as a hard, flat, grayish-looking ulcer that does not heal. Another appears as a firm red patch and still another as a cauliflowerlike growth. There may be hair loss around the tumor because of constant licking. Squamous carcinomas invade locally and metastasize at a late stage to the regional lymph nodes and lungs.

Melanomas arise from melanin- producing cells in the skin. They are more common in Scottish Terriers, Boston Terriers and Cocker Spaniels. These brown or black nodules are found on darkly pigmented areas of skin, particularly on the eyelids. Rarely, you will find an unpigmented melanoma. They also occur on the lips, in the mouth, on the trunk and limbs and in the nail beds. Melanomas on the skin are usually benign: those in the mouth are highly malignant. About 50% of nail bed melanomas are malignant and metastasize. Metastases occur in the regional lymph nodes, lungs and liver.

Perianal growths are usually benign cancers that appear around the rectum, especially in unneutered male dogs. Rarely, these will be malignant perianal adenocarcinomas. Siberian Huskies are predisposed to this type. Anal sac gland tumors are a separate entity. These types of tumors are often aggressive and malignant. They arise from the anal glands on either side of the rectum and often metastasize quickly.These cancers are also associated with an increase in calcium in the blood.

Sarcomas are malignant tumors that arise from various sources, including connective tissue, fat, blood vessels, nerve sheaths and muscle cells. Collectively they account for about 15% of all cancers in dogs. There is a genetic disposition among German Shepherds, Boxers, Saint Bernards, Basset Hounds, Great Danes and Golden Retrievers. Sarcomas occur on the surface of the body and within organs. They tend to grow slowly and metastasize only when they have been present for some time. Metastases usually involves the lungs and liver. Some sarcomas are well defined and appear to be encapsulated, others infiltrate the surrounding tissue and have no distinct margins. Sarcomas within body cavities often grow to a large size before being discovered. Soft tissue sarcoma is diagnosed using X-rays, ultrasonography, CT scan and tissue biopsy.

Hemangiosarcoma - arising from cells that make up the lining of small blood vessels

Lymphoma - arising in lymph nodes and in organs that contain lymphoid tissue, such as the spleen, liver and bone marrow

Lymphoma, also called Lymphosarcoma, is a type of cancer that arises (often simultaneously) in lymph nodes and in organs that contain lymphoid tissue, such as the spleen, liver and bone marrow. The disease affects middle-aged and older dogs. It should be suspected when enlarged lymph nodes are found in the groin, armpit, neck or chest. Affected dogs appear lethargic, eat poorly and lose weight. The liver and spleen are often enlarged. Chest involvement results in pleural effusion and severe shortness of breath. Skin involvement produces itchy patches or nodules on the surface of the skin that mimic other skin diseases. Intestinal involvement causes vomiting and diarrhea. A complete blood count may show anemia and immature white blood cells. The serum calcium is elevated in 20% of dogs with lymphoma. Blood and liver function tests are usually abnormal. A bone marrow biopsy is helpful in determining if the disease is widespread. Chest and abdominal X-rays and ultrasonography are particularly valuable in identifying enlarged lymph nodes, organs and masses. A diagnosis can also be made by fine needle aspiration of an enlarged lymph node. In questionable cases, the entire lymph node should be removed for a more complete evaluation.

Hemangiosarcoma is a tumor of the vascular tissues. This cancer may be noticed as a lump on a rib or an abdominal swelling, but can progress unnoticed while growing on the heart, liver or spleen. The cancerous growths are quite fragile and often break off, "seeding" cancer throughout the body. Alternatively, the first sign may be sudden death as a large area of tumor ruptures and the dog bleeds to death internally.

This is a common urinary tract cancer, especially in older female dogs. The first signs may be similar to a urinary infection: straining to urinate or passing some bloody urine. Diagnosis may require special dye studies (that could cause cancer as well). Scottish Terriers are predisposed to this cancer, especially if they have been exposed to lawn care chemicals that contain 2,4D.

Bone tumors can be either malignant or benign. Osteosarcoma and chondrosarcoma and are the two most common malignant bone tumors. Osteomas and osteochondromas are the most common benign types.

Osteosarcoma is by far the most common malignant bone cancer in dogs. This cancer affect dogs of all ages, with a median age of 8 years. It occurs with equal frequency in males and females. Giant breeds, such as the Saint Bernard, Newfoundland, Great Dane and Great Pyrenees are 60 times more likely to develop an osteosarcoma than are dogs weighing less than 25 pounds. Large breeds, such as the Irish Setter and Boxer, are eight times more likely to develop osteosarcoma. Toy breeds are rarely, if ever, affected. Osteosarcoma occurs most often in the bones of the front legs, followed, in order of frequency : by the hind legs, the flat bones of the ribs, and the mandible. Often, the first sign is a limp in a mature dog who has no history of injury. Usually this receives little attention until swelling of the leg or a bone mass is observed. Pressure over the tumor causes pain. Fractures can occur at the tumor site. X-rays can strongly suggest the disease, but a definitive diagnosis depends on biopsy of the tumor. Osteosarcoma is an aggressive cancer that quickly spreads to the lungs.

Chondrosarcoma is the second most common malignant bone tumor in dogs. The average age of onset is six years. This tumor tends to involve the ribs, nasal bones and pelvis. It presents as a large, hard, painless swelling in an area containing cartilage. This tumor also metastasizes to the lungs, but is less aggressive than osteosarcoma.

Ostemas are raised tumors composed of dense but otherwise normal bone. They occur about the skull and face.

Osteochondromas: also called multiple cartilaginous exostoses, are bone tumors that arise in young dogs from areas where cartilage grows prior to calcification. Osteochondromas may be single or multiple and are found on the ribs, vertebrae, pelvis and extremities. There is a hereditary basis to osteochondromas. A bone biopsy should be performed to determine the type of bone tumor, unless the appearance on X-ray is conclusive.

Testicular tumors are common in male dogs. Most affected dogs are over 6 years of age, with a median age of 10. The majority of tumors occur in undescended testicles-located in the inguinal canal or abdominal cavity. In fact, tumors develop in up to 50 percent of undescended testicles is characteristic of a testicular tumor (although the mass may simply be the undescended testicle). Tumors in descended testicles are less common. The affected testicle is often larger and firmer than its neighbor and has an irregular, nodular surface. At times the testicle is normal size but feels hard. The three hard testicle tumors in dogs are sertoli cell tumors, interstitial (leydig) cell tumor, and seminomas are malignant. Some sertoli cell tumors produce estrogen, which can result in feminization of the male with enlargement of the mammary glands, a pendulous foreskin and bilateral symmetric hairloss. A serious a complication of high estrogen levels is bone marrow suppression. Ultrasonography is particularly useful in locating undescended testicles and determining whether a scrotal mass is a tumor, abscess, testicular torsion or scrotal hernia. Fine needle aspiration biopsy provides information on the cell type of the tumor.

An unusual neoplasm called transmissible venereal tumor occurs in both males and females. Tumor cells are transplanted from one dog to another, primarily during sexual contact, but also through licking, biting and scratching. Transmissible venereal tumors tend to occur in free-roaming dogs, particularly those living in urban areas. They appear within seven days of contact exposure. Transmissible venereal tumors are solitary or multiple tumors that usually appear as cauliflowerlike growths or as nodules on a stalk. The growths may be multinodular and/or ulcerated. In females, transmissible venereal tumors develop in the vagina and on the vulva. In males, they occur on the penis. Other locations in both sexes include the skin of the preineum, face, mouth, nasal cavity and limbs. Transmissible venereal tumors are considered low-grade cancers. They do have the potential to metastasize, although this is rare.

The vaginal and vulva areas are the most common sites for tumors of the female genital tract. These tumors tend to occur in older, sexually intact females, at an average age of 10 years. Benign tumors include leiomyomas, lipomas and transmissible venereal tumors. They are often found on a narrow base or a long stalk. Malignant tumors in this area are rare. They include leiomyosarcomas, squamous cell carcinomas and mast cell tumors. Malignant tumors grow locally, infiltrate surrounding tissue and become quite large. They rarely metastasize. Signs include vaginal discharge or bleeding, a mass protruding through the vulvar lips, frequent urination and excessive licking at the vulva. Large vaginal tumors can cause swelling and deformity of the perineum, block the birth canal and cause problems in whelping. Note a mass protruding through the vulva of a bitch in heat is most likely to be due to vaginal hyperplasia

Ovarian tumors are uncommon. Most cause no symptoms and are found incidentally during a spay operation. Occasionally, a tumor becomes large enough to produce a visible or palpable swelling in the abdomen.

Papillary adenoma is a benign tumor that may arise simultaneously in both ovaries. A malignant variety, called papillary adenocarcinoma, is the most common ovarian cancer in bitches. These tumors spread thoughout the abdominal cavity and are associated with ascites.

Granulosa cell tumors can also become quite large. Some secrete estrogen, producing signs of hyperestrogenism with abnormal heat cycles, enlargements of the vulva and a greasy skin and coat. Other tumors of the overies also occur. Abdominal ultrasonography is particularly helpful in determining the size, structure and location of ovarian tumors. Finding ascites and masses in the abdominal cavity suggests malignancy.

The mammary glands in female dogs vary in number and can be determined by counting the nipples. The typical bitch has 10 mammary glands, five on each side of the midline, begining on the chest and extending to the groin. The largest glands are located near the groin. Mammary gland tumors are the most common tumors in dogs. In fact, among unspayed females the risk of a mammary tumor is 26 percent. This is three times the risk of breast tumors in women. Most mammary gland tumors occur in bitches over 6 years of age (the average age is 10). Forty-five percent are cancerous and 55 percent are benign. An increased incidence occurs in sporting breeds, Poodles, Boston Terriers and Dachunds. Multiple tumors are common. If a bitch has one tumor, she is three times more likely to have or develop a second tumor. The principal sign is a painless lump or mass. Most lumps occur in the larger glands closest to the groin. A mass may be large or small, with boundries that are distinct or indefinite. Some lumps are freely movable, while others adhere to the overlying skin or underlining muscle. Occasionally, the mass ulcerates the skin and bleeds.

Inflammatory cancer is a rapidly progressive neoplasm that spreads throughout the chain of mammary glands and into surrounding skin and fat. Death usually comes in a matter of weeks. Inflammatory cancer may be difficult to distinguish from acute septic mastitis. Malignant tumors spread widely, primarily to the pelvic lymph nodes and lungs. Before embarking on treatment, a chest X-ray should be taken to rule out lung metastases, present in 30 percent of these cancers. Ultrasonongraphy is useful in determining whether the pelvic lymph nodes are involved. Biopsy of the tumor may not be neccessary if surgical removal is contemplated. Inflammatory cancer, however, must be biopsied, because there is little to be gained in attempting aggressive treament in these tumors.

Leukemia is a cancer involving the blood elements in the bone marrow, including the lymphocytes, monocytes, platelets, eosinophils, basophils and erythrocytes. All of these cells can give rise to cell-specific leukemias. For example: lymphoid leukemia is a malignant transformation of the lymphocytes or white blood cells. Leukemia is further subdevided into acute and chronic stages. Both stages are relatively rare in dogs. Leukemia generally occurs in middle-aged dogs. Signs are non-specific and include fever, loss of appetite, weight loss and sometimes anemia with pale mucous membranes. Usually the disease is discovered when blood tests are drawn to diagnose these symptoms. Leukemic cells may or may not be found circulating in the blood. A bone marrow biopsy confirms the diagnosis.