by Dr. Elizabeth Ellis, DVM
Cancer in our companion pets is just as commonplace as it is in humans. In fact, according to the Animal Cancer Foundation, one in every four dogs and one in every five cats will develop cancer in their lifetime. Many of the cancers that afflict our pets are the same that affect humans. Cancer can arise from any tissue and results when cells divide more rapidly than normal or don’t die when they should.
The 5 most common cancers
In dogs, the five most-common cancer are: lymphoma, hemangiosarcoma, osteoscarcoma, mast cell tumors, and melanoma.
- Lymphoma or lymphosarcoma accounts for almost a fifth of all cancers in dogs. It can affect any breed at any age, however, some dogs such as the golden retriever are genetically predisposed. The most-common presentation is enlarged lymph nodes on the outside of the body, especially behind the knees, in front of the shoulders and under the jaw. These will appear as firm swellings under the skin in these areas to an owner. Another type of lymphoma causes the lymph nodes or lymph tissue inside of the body to enlarge, causing vomiting, diarrhea or difficulty breathing. Lymphoma can be very aggressive and without proper diagnosis and treatment, dogs can die in a few short weeks. Ideal treatment consists of multi-drug chemotherapy, permitting most dogs to respond and enjoy good quality of life for another year to year and a half. Single drug therapy with a steroid such as prednisone can also be used, allowing the dog to feel much better for a few months before signs return.
- Hemangiosarcoma is a tumor that originates from blood vessels and generally affects middle-aged to older dogs. Although any breed can be affected, we frequently see it in golden retrievers and German shepherds. The tumor most commonly affects the spleen (an organ inside of the belly) and usually grows slowly, hidden in the belly from the watchful eyes of owners. It is non-painful and often the dog shows no signs of illness until late in the disease when internal bleeding occurs due to the tumor rupturing. At that point, the dog suddenly appears in shock with weakness, pale gums, and difficulty breathing. The tumor can also spread to the heart, liver, and skin. Treatment includes surgery to remove the spleen and control bleeding, and sometimes also includes a blood transfusion. After surgery, chemotherapy is started however even with aggressive treatments, many dogs do not survive longer than six to nine months.
- Osteosarcoma is a cancer of the bone, usually affecting the long bones in the legs; however, it can also originate in the ribs or skull. It is generally seen in giant dog breeds such as the great Dane at seven to ten years of age. It is a very aggressive cancer that can spread throughout the body rapidly. It is often first noted by owners as a firm swelling under the skin or by a limp in a leg. Treatment includes amputation of the affected leg to remove the tumor then chemotherapy to treat metastasis (spread) within the body. With surgery alone, dogs usually only survive four to six months however can live up to one year with chemotherapy added. Newer procedures are being utilized to give these dogs prosthetic limbs or even limb-sparing techniques in which artificial bone replaces the removed cancerous bone.
- Mast cell tumors are very common tumors, which can be found on the skin and can spread to the liver and spleen. They can occur on any dog breed at any age but are more frequently seen in boxers and bulldogs. They originate from mast cells, which are immune cells involved in allergic reactions. Often mast cell tumors are misdiagnosed, as they can masquerade as many other inconsequential masses, such as a small soft swelling under the skin resembling a fatty tumor or a tiny dark mass on the outside of the skin appearing as a skin tag. They are, however, easy to diagnose with a fine-needle aspirate by your veterinarian. Treatment generally involves a large and aggressive surgical removal of the tumor. Depending on the grade of the tumor (which tells how aggressive the tumor is), additional chemotherapy may be recommended. When a low- or moderate-grade mast cell tumor that hasn’t spread is removed properly, the dog generally has a normal lifespan and is considered cured.
- Melanoma is a tumor of pigmented skin found anywhere on the body, including the mouth. It is more commonly seen in dogs with dark-hair coats such as the Scottish terrier or doberman pinscher. Treatment depends on where the tumor is and if it has spread to a lymph node. Generally, surgical removal of the mass followed by radiation therapy or chemotherapy is recommended. Newer treatment protocols include surgical removal followed by a melanoma vaccine available through veterinary oncologists.
In summary, dogs can be affected by many of the same cancers as us. You should check your dog for lumps and bumps frequently, and if any are noted, take your dog to your veterinarian for a more in-depth examination and diagnosis. Additionally, if your dog has weakness, vomiting, limping or other signs which may be associated with cancer, you should have him examined. Your veterinarian can give you specific information regarding treatment options, prognosis, and quality of life for your pet.
Dr. Elizabeth Ellis, DVM, appears courtesy of Aspen Ridge Animal Hospital in Lakeside.
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