Cancer in Dogs - Kinds, Treatments and Prognosis

Cancer

Cancer in dogs can affect everything from the skin to the bones. The disease is caused by uncontrolled cell growth and can take one of two forms: benign (does not grow in an unlimited, aggressive manner, does not invade surrounding tissues and does not spread to other parts of the body) and malignant (meaning it enters healthy tissues, grows aggressively and spreads to other areas of the body.) Since some cancers grow slowly while others develop more quickly, be sure to consult your veterinarian as soon as possible if you notice anything unusual.

Types of Cancer

There are several different types of cancer in dogs. The following are some of the most common, including their symptoms and treatments:

* Hemangiosarcoma (HSA)- An aggressive, malignant cancer that arises from the blood vessels and mostly affects the spleen, heart or skin. The skin form is associated with sun exposure and white haired breeds are at greater risk. The lesions look like dark red or black growths on the skin and should be removed immediately since 1/3 will spread internally. Hemagiosarcoma of the spleen and heart usually present with acute collapse/ weakness and pale gums due to bleeding of the tumor. German shepherds, golden retrievers, boxers and English setters seem to be predisposed. Surgical removal of the spleen and biopsy is needed to diagnose HAS, since the mass may benign (hemangioma or hematoma). Surgery to remove the heart mass or open up the lining of the heart is only palliative and often the mass is not resectable. While early and aggressive treatment, including chemotherapy, can prolong your dog's life, complete remission is rare.
Cutaneous Histiocytomas - Small, round benign tumors that can appear anywhere on the body's skin, but are most common on the head, ears and neck of dogs less than 3 years of age. They usually regress in 2-3 months, however, if the tumors bother your dog, they can be surgically removed. This tumor has been reported to be the most common skin cancer and the most commonly observed form of cancer overall.6,7

Lymphoma (LSA) - A common, malignant cancer (about 10-20% of all cancers in dogs) that occurs in the lymph nodes, spleen, liver and other organs, affecting primarily middle-aged and older dogs. Certain breeds like rottweilers, Scottish terriers and golden retrievers are at increased risk and there is also some speculation that it may run in families. The tumors in the lymph nodes appear as swellings, but other symptoms vary depending on the portion of the body involved: the gastrointestinal form of this cancer causes vomiting, diarrhea and weight loss, the chest form leads to shortness of breath and muffled heart sounds, and the skin form causes itchy red lumps to appear on the skin and inside the mouth. Biopsies, X-Rays and ultrasounds are used to diagnose lymphoma. Once diagnosed lymphoma should be staged in order to determine best course of treatment and provide a prognosis. Treatment often consists of chemotherapy +/- surgery. Some veterinary hospitals are now offering a bone marrow transplant, but the cost (around $20,000) will likely prohibit most us from pursuing it. A consultation with a veterinary oncologist can determine the best course of treatment, which can sometimes add a year or more to a dog's life.
Mammary Cancer - Most common cancer in female dogs and predominantly affects older female dogs between five and ten that have not been spayed. German shepherds, cocker spaniels, poodles and terriers are overrepresented. Half of these tumors are malignant and half of these have spread at the time of diagnosis. The tumors can affect one or more of the mammary glands along the belly of your pet. They can be a single small mass or be multiple large ulcerated masses. Malignant tumors usually grow rapidly, and benign tumors are typically slow growing. A biopsy and microscopic investigation will determine if the tumors are benign or malignant. Prompt surgical removal of any mammary tumor is recommended. If caught early enough, surgical removal of the tumors can completely eliminate over 50 percent of malignant cases. Spaying is also recommended if not already done since 50% of malignant tumors and some benign tumors have receptors for female hormones. Early spaying (before the first heat) reduces the risk of developing mammary cancer. Sometimes chemotherapy is also used in the treatment of some mammary cancers. Prognosis depends on type of cancer, size of the mass, extent of spread, ulceration, how fast it grows and the biopsy results.
Mast Cell Tumors (MCT)- These are a common skin tumor (20% of all skin tumors in dogs) found anywhere on the skin, especially the trunk. boxers, Boston terriers, bullmastiffs and English setters are predisposed. MCT vary in appearance and can be smooth, bumpy or ulcerated. They can also get bigger or smaller over a short period of time, especially when touched due to the compounds in MCT (histamine and heparin) causing redness and swelling. Most MCT are locally invasive and often difficult to remove. These tumors are graded I-III, based on their behavior (invasiveness, how well differentiated it is, how quickly it is dividing etc) and the higher grades are staged. MCT typically spread to lymph nodes, liver, spleen and bone marrow so staging requires blood work, x-rays, ultrasound, lymph node aspirates, bone marrow aspirates. Surgical removal +/- radiation therapy is the main treatment and require wide margins. Chemotherapy is sometimes used but response is unpredictable. Prognosis is good for grade I and II and the prognosis for dogs with grade III is guarded. Dogs that develop MCT are likely to develop more, therefore need to be watched closely.
Osteosarcoma (OSA)- Most common bone tumor in dogs. It is an aggressive, malignant, highly metastatic bone tumor most often occurring in the bones around the shoulder, wrist and knee but can develop in any bone. It primarily affects older large or giant breed dogs, with great danes, Saint Bernards, great Pyrenees, Newfoundlands, Bernese mountain dogs and Irish wolfhounds being at greatest risk. The tumors usually produce pain, lameness and swelling in the affected limb. Sometimes they present as a fracture. A biopsy is done to identify the cancer and because of the high metastatic rate, chest x-rays are also indicated. Other tumors can mimick OSA like Chondrosarcoma, Squamous Cell Carcinoma and Synovial Cell Sarcoma. Fungal infections can have similar symptoms, so fungal titers should also be done if there is possible exposure. Treatment options include amputation, radiation, chemotherapy and pain medications depending on if you want to alleviate pain or try for a cure. Prognosis depends on many factors and survival times vary from 3 months to 2 years.

Cancer can be a devastating diagnosis. Even if your pet has been diagnosed with cancer, fight it with the positive power of nutrition. Nutrient rich foods that will give your dog the best opportunity to be healthy, like Prescription Diet n/d can create a powerful platform from which your dog can fight cancer.

Tim Kilroy is a writer living in Boston. He has a Labradoodle that demands only the best pet supplies.

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