Information about Tumors and Cancers in Dogs

(slightly adapted from: WebMD)

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 categories: benign and malignant. Benign tumors grow slowly, don’t invade or destroy neighboring tissue, and don’t spread to other parts of the body. These cancers aren’t usually life-threatening. They are cured by surgical removal, provided that the entire tumor can be removed. Malignant tumors are potentially 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 veterinarian. 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. Bone 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 gastrointestinal 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 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.

Besides stomach cancer, the most common cancers in Belgian Shepherds are lymphosarcoma, hemangiosarcoma, and osteosarcoma.

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 cells 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. Belgian Shepherds have a high incidence of stomach cancer.

A number of genes have been identified as 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 suppress 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.

Carcinogens are environmental influences known to increase the likelihood 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 of 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 seldom a connection. Trauma causes hematomas, bruises, and contusions, but does not cause abnormal cell growth. However, an injured site is usually examined closely, and small preexisting tumors are sometimes discovered this way. Some veterinarians believe 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.

Stomach cancer

According to American figures, Belgian Sheepdogs (Groenendaels) are 16 times more likely to develop gastric carcinoma, compared to other breeds. Belgian Tervurens weigh in at 12 times more likely. European information tend to show more Belgian Tervueren with stomach cancer than Groenendaels. A Norwegian study on dogs with cancer indicated that Tervuerens are 56 times more likely and Groenendaels are 34 times more likely to develop stomach cancer than average breeds. Both American and European studies indicate a genetich predisposition.
Malinois and Laekenois do not appear to have this genetic predisposition at this time, but with inter variety breeding it might pop up in time.

Gastric carcinoma often shows up with a loss of appetite and/or vomiting. Many dogs show weight loss. Often signs are not obvious until dogs have an advanced stage of the cancer. Then it is often a matter of weeks before the dog has to be put to rest.

Stomach cancer tends to show up in middle aged dogs - often 6 years old or older.

The definitive diagnosis should be made using a surgical or endoscopic biopsy. An ultrasound may show early signs, but this method can't exclude ulcers and other stomach problems, which give similare symptoms.

Stomach cancer is almost always inoperable. Medication can sometimes stretch the lifetime of the dog, but mostly this is not much more than weeks or months. So far, gastric carcinoma is fatal.

Useful links Stomach Cancer:

Scientific papers Stomach Cancer:

Treating Tumors and Cancers in Dogs

The best possible treatment option is surgical removal of a cancer that has not spread. To prevent recurrence, a surrounding margin of normal tissue should also be removed. An initial approach that removes the tumor with an adequate margin of normal tissue may be the most important factor in controlling cancer. When a cancer recurs locally because of incomplete excision, the opportunity for cure is often lost. That’s why surgeons speak of “clean margins,” meaning no cancer cells are found on the outer edge of the tissue removed.

A cancer that spreads only to local lymph nodes may still be cured if all the involved nodes can be removed along with the primary tumor. Even when a cancer is widespread, removing a bleeding or infected mass, or simply a large one that is interfering with a normal physical function, can provide relief and temporarily improve the quality of life.

Electrocautery and cryosurgery are two techniques by which tumors on the surface of the body can be removed. Electrocautery means burning off the tumor using electricity; cryosurgery involves freezing the tumor to remove it. These methods provide an alternative to surgical removal and are suitable for benign tumors such as papillomas. New surgery techniques may use lasers or hyperthermy-heat treatment. Radiation therapy is used primarily for local tumors that have not metastasized. Many canine tumors are sensitive to radiation. They include mast cell tumors, transmissible venereal tumors, squamous cell carcinomas, cancers of the oral and nasal cavities, and soft tissue sarcomas. A potential disadvantage of radiation therapy is that it requires special equipment and must be done at a medical center. Radiation therapy can also be done to relieve pain, especially with very painful cancers such as osteosarcoma (bone cancer).

Chemotherapy is used to prevent and control the metastatic spread of cancer cells. However, most canine cancers are only moderately sensitive to chemotherapy. It can cure only one type of cancer in dogs: transmissible venereal tumors. When used as the only form of treatment, chemotherapy usually does not extend survival. Lymphosarcoma and leukemia are exceptions. Chemotherapy drugs, even when their use is tightly controlled, can have major side effects. In humans, chemotherapy is aimed at achieving a cure. Due to their lesser efficacy in dogs, chemotherapy is aimed at controlling the disease and giving the dog a period of remission. Lower dosages are generally used and many dogs do not have the severe reactions to chemotherapy that people do.

Useful links other cancers:

Other useful links:

Specific health records:

Databases with health records:

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