One in four dogs will be diagnosed with cancer in their lifetimes, and it’s the leading cause of death in pets beyond middle age. As with people, some canine cancers are more common than others. Fortunately, with treatment, many dogs can continue to live quality lives after a cancer diagnosis.
Lymphoma in Dogs
Canine lymphoma is one of the most common cancers seen in dogs today, accounting for up to 24% of all new canine cancers. The most common form of lymphoma in dogs is the involvement of one or more of the external lymph nodes.
Many dogs may not feel sick or may have only very mild signs such as tiredness or decreased appetite. Other dogs may have more severe symptoms such as weight loss, vomiting, diarrhea, excessive thirst or urination, weakness, or difficulty breathing. The severity of the signs depends upon the extent of the disease and on whether the cancer has caused changes in organ function. Often, the only noticeable sign is an enlargement of the lymph nodes under the neck, behind the knees, or in front of the shoulders. Other organs, such as the liver, spleen, and bone marrow, can be involved as well.
Canine lymphoma is initially very sensitive to chemotherapy. Up to 95% of dogs treated will go into remission when the most effective treatment protocols are used.
Osteosarcoma in Dogs
The most common primary bone tumor in dogs is osteosarcoma and accounts for 85% of all skeletal tumors. Osteosarcomas are highly aggressive tumors, characterized by painful local bone destruction and distant metastasis (spread to other organs). Osteosarcoma commonly affects the limbs of large or giant breed dogs but can also occur in other parts of the skeleton (skull, ribs, vertebrae, pelvis).
The signs associated with a bone tumor may be nonspecific. Tumors in the limbs often cause various degrees of lameness and pain, and a firm swelling may become evident as the tumor size increases. It is common for pain to be intermittent initially, and it may improve initially with pain medications. As the degree of discomfort increases, it can cause other signs such as irritability, aggression, loss of appetite, weight loss, sleeplessness, or reluctance to exercise. Some dogs may present to the veterinarian as a result of a fracture due to weakening of the affected bone.
Treatment recommendations for bone tumors depend on multiple factors, and a complete physical examination and additional testing may be necessary to determine the most appropriate treatment for an individual dog.
Mast Cell Tumors
Mast Cell Tumors are the most common skin tumors in dogs. Mast cell tumors can look and feel like anything, so it is impossible to diagnose without looking at cells under the microscope. After close examination, a grade of malignancy is assigned. The grade suggests how the tumor will behave and the best course of treatment. Low or intermediate-grade tumors are unlikely to spread, and surgery may be the only treatment required. High-grade tumors have a greater chance of spreading, so veterinary oncologists look very carefully for metastasis and consider using chemotherapy in addition to surgery. Radiation therapy is another option for some cases.
Oral Melanomas in Dogs
Melanomas are tumors arising from pigment cells. In dogs, they most commonly occur on the skin, in the mouth, and on the toenails. While the majority of skin melanomas are benign in dogs, the majority of oral and toenail melanomas are malignant, with the potential both to invade local tissue, to regrow after surgery, and to spread to other parts of the body.
Most melanomas in the mouth or skin will present as dark, raised masses. Melanomas in the mouth can be associated with drooling, foul odor, bleeding from the mouth, or difficulty eating. Those occurring on the toenail can cause toe swelling, loosening of the affected toenail, or lameness on the affected leg. Diagnosis of melanoma will usually require a fine needle aspirate or biopsy.
Surgery is the first line of defense for melanomas. Dogs that receive an aggressive surgery first (to minimize the likelihood of leaving microscopic tumor cells behind) may do better than those undergoing conservative surgery. Tumor recurrence or spread (metastasis) is likely. In cases where surgery is not possible, radiation therapy, chemotherapy, or immunotherapy can sometimes be effective.
Hemangiosarcoma in Dogs
Hemangiosarcomas are malignant tumors derived from the cells lining blood. Since blood vessels occur throughout the body, hemangiosarcoma can appear anywhere. The most common sites are the spleen, liver, and heart. It happens less commonly in the skin.
Typically, hemangiosarcomas are both locally aggressive and have a high likelihood of spreading to other parts of the body. These tumors are usually filled with blood and very fragile. Dogs with hemangiosarcoma tumors inside the body may have signs related to blood loss into the abdomen or the space around the heart, resulting in weakness, lethargy, or pale gums. Dogs with cutaneous hemangiosarcoma may simply have a mass in or under the skin. Some of these cutaneous tumors may occur in light-skinned dogs as a result of sun exposure.
The majority of dogs with hemangiosarcomas inside the body will develop problems related to tumor spread (metastasis) in the future. On average, metastasis is detected 1-3 months after surgery if not combined with chemotherapy.
Despite these treatments, the long-term prognosis for dogs with hemangiosarcoma is generally poor. Average survival times with surgery and chemotherapy are approximately 5-7 months, with only 10% of dogs surviving for one year. Dogs with the subcutaneous (under the skin) form of hemangiosarcoma may do somewhat better than this average.
Transitional Cell Carcinoma in Dogs
The most common tumor type of the urinary system in dogs is transitional cell carcinoma (TCC). TCC is most often located in the trigone of the bladder, where the ureters coming from the kidneys and the urethra intersect but can happen in any part of the urinary system, including the prostate gland in male dogs.
A complete diagnostic work-up, including blood work, imaging, and biopsies, is recommended before pursuing treatment. Based on diagnostic results, treatment options may include surgery, radiation, and/or chemotherapy.
Treatment for Pets with Cancer
Forty years ago, pets with cancer had few options. Today, veterinary oncology specialists around the country offer a variety of treatments. The Flint Animal Cancer Center’s comprehensive clinical practice offers advanced treatments in chemotherapy, surgery, and radiation for both common and rare cancers. The FACC also offers veterinary medicine’s largest clinical trials program. The One Cure clinical trials program enrolls client-owned animals to evaluate the effectiveness of new drugs, find novel uses of old drugs, or investigate new approaches to surgery and/or radiation therapy to treat cancer.
If you are concerned that your pet might have cancer, the best place to start is with your local veterinarian.