Volume No. 17 Issue No. 10 October 2020  

Dr. Jim Humphries
  Melanoma in dogs
  Dr. Jim Humphries

     You might find this surprising: about one in four dogs will, at some stage in their life, develop cancer. Almost half of dogs over the age of 10 will develop cancer. Dogs get cancer at roughly the same rate as humans, while there is less information about the rate of cancer in cats. Some cancers, such as lymphoma, are more common in cats than in dogs.
   We’ve been looking at the most common types of cancer in pets for the past several months. This month, it is melanoma. This is a malignancy of the cells that produce pigment in the body, and those cells are called melanocytes. This cancer is much more common in dogs than cats. They can occur in all parts of the body, but their behavior is very different depending on where they start.
   About 80 percent of melanomas will be diagnosed in the mouth. They are typically seen in dogs 10 years and older. These typically look like a single dark bump, but they can extend into underlying soft tissue and bone. They also can be pink and appear flat on the skin, making them hard to see at first. Most are diagnosed at the time of a complete dental cleaning and exam.
   Oral melanomas are aggressive tumors and have a high rate of movement or metastasis to local lymph nodes and the lungs. Even if we remove all the oral tumor, about 85 percent of these dogs will develop metastasis or spreading of the cancer to other parts of the body. A spreading cancer is sometimes referred to as a “metastatic cancer” or “metastatic disease.”
   The next most common-place melanoma is found in the toes. These occur in about 20 percent of dogs, and they act like an oral melanoma. They can move to the local lymph nodes that drain the leg and cause serious disease there.
   In people, we normally think of melanoma as a dark spot on the skin due to sun exposure. Melanoma of the skin in dogs looks the same but is usually seen only on the haired skin, and they are usually benign so complete surgical removal is often the cure.
   A biopsy is often needed to gain more information about how this particular mass will develop. The mass can be “staged” by the pathologist to let the veterinarian know how aggressive it will be.
   The most common initial treatment for melanomas is surgical removal if at all possible. Dermal melanomas can often be easily removed with local surgery. However, metastasis is common and only about 10 percent of dogs will survive more than a year. This is where recent advancements come into play. There is a melanoma vaccine called Oncept® — a DNA vaccine that makes the dog mount an immune response against any remaining cells.
   Overall, dogs with malignant melanoma who are treated with surgery alone show a survival time of about four to six months. They will eventually develop life-ending disease in the local lymph nodes and lungs. If the Oncept® vaccine is given after surgery, the median survival time goes up to 1.5 years, with 30 to 40 percent of dogs surviving more than two years. Dogs with tumors located on the lip are more likely to experience longer survival times compared to tumors in other locations. Much depends on the staging of the biopsy by the pathologist.
   As always, if you see something, say something. Any lump or bump that is persistent or grows should be seen by your veterinarian. The visit might be a short exam and nothing serious. But in the outside chance it is serious, early is the time to act.

   Dr. Jim Humphries is a veterinarian and provides hospice and end-of-life care for pets in the Colorado Springs area. He also serves as a visiting professor at the College of Veterinary Medicine at Texas A&M University. He lives in Falcon with his wife, horses and Great Danes. https:// www.HomeWithDignity.com
Canine melanoma on the skin— human melanoma on the skin
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