To Vaccinate or Not to Vaccinate: That is the Question
You may think that talking about vaccinations is out of my wheel house as I am an oncologist, not a primary care veterinarian, but you would be wrong! No, I’m not going to open the vaccines for children can of worms (and for more information on worms see Dr. Holland’s last blog post), rather we are going to talk about the vaccines available for cancer patients. Yes, there are cancer vaccines available, but they are used in patients that have already been diagnosed with cancer as unfortunately, these vaccines will not prevent cancer.
The immune system is a wonderful thing. It protects us from many things that are attempting to do us harm, including bacteria, viruses, and even cancers. When we administer chemotherapy to a cancer patient, we are attempting to reduce the number of cancer cells in the body to a point that the immune system can take over and kill off those that remain. There isn’t a magic number of cells that the immune system can handle, but many believe that the number needs to around 1,000 for the immune system to do its thing. Considering that a palpable tumor has 10^9 cancer cells (that is one billion!), you can see that this is no small feat. This is the reason that most patients need to undergo surgery first, and in some cases also receive chemotherapy to have the best outcomes. It is also why the available cancer vaccines can’t be used alone to achieve maximum control of the tumor. There is simply too much disease present for the immune system to be effective at ridding the body of anything, even with the amped up response that a vaccine can induce.
Cancer vaccines have been studied for quite some time in human and veterinary medicine. Some have been successful, but most have not. There are a couple of companies that currently offer autologous (meaning that the cells are taken from the patient) cancer vaccines for veterinary patients. To make these vaccines, the tumor or parts of the tumor, are removed and sent in by the veterinarian. The company then uses cells from the tumor to make a vaccine to be given back to the patient. While this may be safe as there is little risk of harm to the patient as the cells are their own, there is NO DATA to say that these are effective. Some studies have been done, but they have used flawed methods, and their results are questionable. There is no oversight into the production and distribution of these vaccines and to date in veterinary medicine, there have been no reported successes other than in dogs with papillomas (which are caused by a virus). In short, I do not recommend administration of these types of vaccines. I do, however, recommend the use of appropriately researched, FDA approved, commercially available cancer vaccines. Luckily, there are a few of these offered for our veterinary cancer patients.
The most well-known of the cancer vaccines is the one available for melanoma. Called Oncept®, this vaccine has been available to treat patients with melanoma for about 10 years. It is the first DNA vaccine approved for cancer treatment in animals, and the technology utilized for this vaccine may be used to develop a melanoma vaccine for humans. Similar to melanoma in humans, melanoma in dogs has a high rate of spread to lymph nodes and lungs, which is ultimately what most melanoma patients die from. Unfortunately, melanoma is generally considered resistant to chemotherapy, with only up to a 30% response rate reported so far. This tells us that the addition of chemotherapy is not likely to prevent the spread of the disease, and is therefore unlikely to add additional benefit. With the addition of the vaccine, many patients will experience a significantly longer life span than they otherwise would have because of the decreased chance of cancer spread. Many dogs with melanoma have a 6 month life expectancy with surgery alone. The addition of the vaccine can improve that life expectancy to 18 months. I believe this vaccine works, I have seen this vaccine work for many of my patients, and I have used it on my own dog. In short, I have and will continue to recommend this vaccine for my patients.
Oncept® isn’t the only veterinary cancer vaccine available. There is also one to treat cat fibrosarcomas, a type of soft tissue sarcoma. These tumors in cats can occur secondary to inflammation that can be caused by an injection. Large surgeries are needed to remove these tumors, and radiation therapy and chemotherapy are often recommended after surgery has been performed. Even with all 3 treatments, many tumors will regrow. A vaccine that expresses IL-2, a molecule (called a cytokine) that signals the immune system to regulate the activity of white blood cells, has been developed to help manage this disease. There have been studies performed in Europe that show a benefit in cats that receive the IL-2 vaccine both before and after surgery; however, data from larger scale studies is not yet available. We also do not know how helpful this IL-2 vaccine is when used only after surgery. I have recommended this vaccine for a couple of my patients, but I believe that further data is needed prior to using this on a larger scale.
A vaccine is for dogs with B-cell lymphoma is also available. This is a DNA based vaccine that targets CD 20, which is a molecule found on the surface of B lymphocytes (the cells that cause the lymphoma). Increasing the body’s recognition and destruction of cells with this molecule may allow patients with lymphoma to live longer than they would have with chemotherapy alone. This vaccine is currently available via conditional licensure from the FDA, which means that it is only approved for use after a full chemotherapy protocol has been administered. The data that has been published on this vaccine so far is minimal. However, more dogs are being studied and we should have updated data soon. As with the IL-2 vaccine, time and results will determine if this vaccine is truly beneficial or not, and if it should be recommended for our patients.
Researchers continue to search for novel ways to use the immune system to help treat cancer. Current studies are investigating the use of vaccines against dog osteosarcoma and hemangiosarcoma, and if effective, these may be game changers in the world of veterinary oncology. As with all treatments, these vaccines may not be indicated for your pet. Consultation with your local veterinary oncologist is the best way to determine if these options are appropriate for your pet’s disease.