Editor’s Note: Melanoma Monday is for dogs, too. To mark this day that is meant to raise awareness about the disease, as well as highlight some of the advancements that have been made, our Vetstreet.com veterinary cancer expert Dr. Ann Hohenhaus traces the development of a novel treatment.

Golden Retriever being examined by a vet

The drive to create a vaccine against melanoma, a serious cancer in dogs, has been going on for years with many successes and failures along the road. In honor of Melanoma Monday, as well as May being National Skin Cancer Detection and Prevention Month, let’s take a look at the history of a major development that is helping veterinarians to fight this disease in dogs.

Vaccine Refresher

You probably already know this, but just to recap, vaccines are given to both humans and pets to provide protection against an infectious disease, such as influenza or parvovirus. Many vaccines typically contain a portion of a disease-causing virus or bacteria (or sometimes a “safe” form of the entire organism). When the vaccine is administered, the immune system is stimulated to fight a particular disease. The vaccine teaches the immune system to make antibodies that will ideally destroy the virus or bacteria should the person or pet become exposed.

This method of sparking the immune system to fight off infectious disease inspired doctors to consider a similar approach to fighting cancer.

Harnessing the Immune System to Fight Cancer

Interest in using a cancer patient’s own immune system to fight cancer in the same way that vaccines help us to fight infectious disease is not new. Physicians in the late 1800’s occasionally noticed that tumors would regress when cancer patients developed a severe infection. That’s because the severe infection “ramped up” the patient’s immune system. Not only did the patient’s immune system control the infection in some cases, but as a side effect, the cancer briefly regressed as well. This led to unsuccessful attempts to cure cancer by inducing infections in cancer patients.

Modern efforts to harness a patient’s own immune system to treat melanoma, a serious cancer in dogs, began in the mid 1980’s. Veterinary researchers found that administering a bacterium, Corynebacterium parvum, to canine melanoma patients improved survival in some by activating the immune system against the bacteria and hitting the melanoma cells as collateral damage from the immune system activation. However, this method of immunotherapy has been largely abandoned in favor of treatments that more specifically target tumor cells themselves.

A different approach to melanoma immunotherapy that was developed about 10 years ago used a vaccine made from the patient’s own immune system. Immune system cells taken from a dog diagnosed with melanoma were mixed in a laboratory with melanoma cells and immune-stimulating compounds. This process helped “program” the immune system cells to attack the patient’s melanoma. However, this “personalized” vaccine was not very practical as the vaccine could only be produced one dog at a time. As a result, it remains a research tool rather than a clinical therapy.

Yet another experimental approach to treatment of melanoma in dogs requires genetic engineering. Genes essential for the production of white blood cells are inserted into melanoma cells grown in the laboratory. When these genetically engineered melanoma cells are injected into canine patients, the white blood cells mount an immune response against the dog’s melanoma and destroy it. Because the injected cells help to initiate an immune response, this is considered another form of vaccination, but it still has not reached the veterinary market.

As we can see, multiple approaches to developing a melanoma vaccine have been tried, but none of these personalized vaccines are in clinical use today. The fact that these vaccines have not reached the market says more about the difficulty of producing personalized vaccines on a large scale for veterinary patients than it does about the ability of personalized vaccines to control tumors, as some of them have been used as therapies in humans.

Wider Reaching Success: Treating Every Melanoma

The opposite of a personalized melanoma vaccine is a vaccine that is effective against every melanoma. In 2001, researchers at Memorial Sloan Kettering Cancer Center and The Animal Medical Center joined forces to develop such a vaccine for dogs suffering from melanoma. Melanoma is a tumor derived from pigment-producing cells. This vaccine targets tyrosinase, an enzyme involved in the production of pigment that is present in all melanoma cells. The vaccine causes an immune system attack on cells containing the tyrosinase enzyme. Since tyrosinase is limited to cells producing the pigment, the vaccine has limited impact on the patient but a big impact on melanoma cells. A clinical trial in dogs diagnosed with advanced melanoma and treated with the vaccine showed that they lived for more than 15 months compared to 5 months for dogs not treated with the vaccine. This vaccine is approved for use in dogs suffering from oral melanoma, although it may also work in other areas of the body where melanoma is occurring.

The long story of melanoma vaccine development shows the hard work and perseverance necessary to develop a new and successful cancer treatment. Fortunately, all this effort has resulted in a new treatment that, when added to traditional therapies of surgery and radiation, can help affected dogs live better and longer.

The immunotherapy approach to cancer treatment will likely be used to treat other cancers in the future. The challenge to cancer researchers is to identify the unique target on the cancer cells that will stimulate the immune system to eradicate the tumor without damaging any other cells. Or, in other words, to find ways to teach your “old” dog’s immune system new tricks!

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