"Cancer" is defined as any malignant, cellular tumor. To understand this definition, we must break it down. A "tumor" is a swelling or other growth of tissue in which there is uncontrolled and progressive cell multiplication. Tumors can be benign or malignant. "Malignancy" is defined as the tendency to progressively worsen and to result in death, usually accompanied by properties of invasiveness and metastasis. "Metastasis" refers to the transfer of disease from one part of the body to another part – essentially, a migration of cells into neighboring or remote tissues. Putting these definitions together, the term "cancer" encompasses a group of diseases that involve an uncontrolled and progressive transformation of normal cells into abnormal ones that becomes invasive, progressively worsens and ultimately spreads. Another word for cancer is "neoplasia," which is defined as the formation of any new and abnormal growth, especially one in which cell multiplication is uncontrolled and progressive.
Causes of Cancer in Dogs
Medical science has not yet discovered the precise causes of the various types of cancer, despite intensive research in both the animal and human realms. Domestic dogs are susceptible to many different types of cancer. These include lymphosarcoma, osteosarcoma, soft tissue sarcomas, mast cell tumors, hemangiosarcoma, oral melanoma and mammary neoplasia, among many others. Each of these can present in a number of ways, with varying frequencies and degrees of severity. Some dog breeds are predisposed to developing certain types of cancers. Certainly, sun exposure can contribute to development of melanoma in dogs as in people. Breast cancer in dogs is much more common in intact females, as testicular cancer is in intact males. Unfortunately, it just is not possible to identify a "cause of cancer" given the current state of medical knowledge.
Prevention of Cancer
Little is known about how to prevent cancer in companion animals. Once the underlying causes of the various cancers are ascertained, prevention will become more realistic. We do know that spaying or neutering can reduce the risk of testicular and mammary gland cancer in domestic dogs.
Early diagnosis of cancer always improves the prognosis. Surgery, radiation and chemotherapy are available at specialized veterinary hospitals to treat cancer in dogs. With prompt diagnosis, aggressive treatment and ongoing management, including pain management and dietary support, many dogs with cancer go on to live long, comfortable and relatively normal lives.
Cancer is one of the leading causes of death in domestic dogs - especially older dogs - which is partially due to the fact that companion animals are living longer with continual improvements in nutrition and veterinary care. How cancer affects a particular dog depends upon the type of cancer and the biological make-up of the individual animal. Meaningful generalizations about the effects of cancer cannot be made. Ultimately, however, most untreated or untreatable malignancies will cause or hasten death.
Symptoms of Cancer
One of the most common signs of cancer in dogs is the appearance of a lump or mass. Usually, the dog does not seem to notice or be bothered by the lump. However, while it may or may not be malignant, any mass is abnormal and should be evaluated by a veterinarian. Other signs of cancer are nonspecific and largely depend upon the site of origin of the primary tumor, the presence of any metastatic lesions in areas other than the site of origin, and whether there has been any rupture or other acute consequence from the disease. Depending on where the cancer is present, the signs can include:
Superficial or subcutaneous skin masses
Lack of appetite (anorexia; inappetance)
Enlarged lymph nodes
Pale mucous membranes
Lameness, swelling around leg joints, pain (osteosarcoma)
Spontaneous bleeding (hemangiosarcoma)
A common consequence of cancer is something called "cancer cachexia," which refers to the severe involuntary weight loss, fatigue, anemia and wasting of body tissues associated with underlying neoplastic disease.
Dogs at Increased Risk
No particular breed, gender or age of dog is especially prone to developing cancer. Of course, older animals tend to develop diseases, including cancer, more often than very young animals, but making generalizations about predispositions to cancer are not particularly helpful. One generalization that does seem accurate is that Greyhounds and male dogs of any large or giant breed are at higher risk of developing osteosarcoma (bone cancer), especially in their lower legs.
Cancer is a general term for a wide variety of disorders. There is no one diagnostic protocol for "cancer." The veterinarian will adopt an appropriate diagnostic plan based on how the particular animal presents. However, cancer is not particularly difficult to diagnose, if owners are willing to go through the steps necessary to confirm that diagnosis.
How Cancer is Diagnosed
When an obvious tumor or mass is identified, the first step in the diagnostic process is to take a sample by a fine needle aspirate and/or a surgical biopsy. The samples will be evaluated microscopically, and skilled pathologists usually are able to identify cancer cells when they are present. Other techniques include taking impression smears of surgical specimens or open lesions, staining and evaluating those samples and surgical removal and histopathological assessment of whole masses. If cancer is suspected, thoracic radiographs (chest x-rays) probably will be taken to assess whether the disease has metastasized (spread) to the lungs. Ultrasound and fluoroscopy are other diagnostic options. A complete blood count, serum chemistry panel and urinalysis can provide the attending veterinarian with additional important information. Of course, only the veterinarian presented with the particular patient can decide upon the most appropriate diagnostic approach.
Because of the huge diversity in cancer types, a meaningful discussion of how to identify cancer cannot really be had in a general fashion. Cancerous cells may be coursing through a dog's blood or localized in a superficial skin tumor. They may be hidden in abdominal masses or multiplying in lymph nodes. They may be in bone or in bone marrow, and they may be on the skin or under the skin. Each type of cancer is diagnosed in a particular way. However, the above diagnostic tools represent the pool from which veterinarians will select their particular techniques in a given case. Thankfully, if caught early enough, there are a number of treatment options for dogs diagnosed with cancer.
Despite the severity and scariness of any cancer diagnosis, many types of canine cancer can be well-managed with timely detection and therapy. Moreover, new treatment options are being developed all the time. The goals of treating cancer are to prevent further metastasis (spreading), remove all cancerous tissue when possible and restore the dog's quality of life. When an owner notices a lump or bump on his dog or otherwise perceives that his dog just "isn't doing right," he should take his pet to the veterinarian as soon as possible.
Treating Cancer in Dogs
Surgery is the treatment of choice for many canine cancers. Localized masses often can be surgically removed and, when detected early, the procedure carries an excellent success rate. Upon removal, the veterinarian will evaluate whether (and if so, how aggressively) the cancer has spread to other organs in the dog's body. The veterinarian will use this information to assess the outlook for the animal and to establish a prospective course of action. The removed tissue will be submitted to a pathology laboratory for determination of the exact type of tumor and whether appropriate surgical margins were obtained when it was removed. When a cancerous mass is removed, the surgeon tries to achieve what are called "clean surgical margins." This means that normal, non-cancerous tissue can be seen microscopically and continuously at all edges of the removed tumor.
In cases where the cancer is inoperable, other treatment options may be available, including radiation, chemotherapy and other biological therapies. Radiation therapy is designed to kill malignant cancer cells by exposing them to high levels of deadly radiation. Similarly, chemotherapy (treatment with drugs) is a way to kill cancer cells, although it usually cannot target specific cells, but rather targets all rapidly-dividing cells in the body. In some cases, veterinarians may use a combination of therapies, such as surgery together with radiation and/or chemotherapy. One of the adverse effects of both radiation and chemotherapy is that many normal cells can be damaged or destroyed by the treatments. Other existing and emerging treatment options for animals with cancer include targeted molecular therapy, immunotherapy, hyperthermia, cryotherapy, phototherapy, photochemotherapy, thermochemotherapy and emerging unconventional or alternative therapies.
Other less traditional techniques that may benefit dogs with cancer, in addition to medical treatment, might include: massage therapy to help reduce pain, overall stress, and improve comfort; possible application of acupuncture and/or acupressure techniques; use of herbal or other non-regulated supplements or homeopathic "remedies"; and other forms of supportive care that may help to ease pain, increase circulation, speed healing and otherwise promote wellness, relaxation and comfort. Some of these adjunct approaches lack controlled studies of their effectiveness and may not have established quality control methods or ways to assess their benefit to dogs with cancer. However, they may be worth discussing with a veterinarian as an add-along to medical therapy.
The goal of any treatment for cancer, of course, is to eliminate only the malignant cells, but it is not presently possible to completely isolate healthy tissue from cancerous tissue during these treatments. Owners can expect to see some side effects in their dogs from both radiation and chemotherapy, including possible nausea, vomiting, diarrhea, weakness, lethargy and lack of appetite.
The prognosis for dogs with cancer is highly variable, depending upon the type of cancer involved, the location of the tumor(s), whether the cancer is malignant and/or has metastasized, whether the disease was caught early or late in its progress, the commitment and financial status of the owner and the body condition, appetite, activity level and overall health of the animal. Thankfully, modern cancer management in domestic dogs goes well beyond mere attempts to remove cancer cells. Nutritional support, pain management, ulcer prevention, gastric protectants, physical therapy, alternative therapies and a number of other supportive techniques can all be key components of managing canine cancer. It is not uncommon for owners of dogs with cancer to spend $2,000 to $10,000 or more on treatment. Owners are entitled to be given all available treatment options regardless of their cost, so that they can make the best decision for their dog given their personal circumstances.