Traditionally, we’ve had three options to defeat cancer in veterinary patients: surgery, radiation, and chemotherapy. In recent years, however, we have begun to do more research into a fourth option: immunotherapy. 

When we think of the immune system, we typically think about its ability to recognize and eliminate infectious disease. In reality, however, the immune system can serve the same role in recognizing and eliminating cancer.

Unfortunately, the process of recognizing and eliminating a tumor is much less straightforward than the process involved in recognizing and eliminating a bacterial infection. Tumors have a number of methods for evading the host immune responses, including the production of immunosuppressive cytokines and the alteration of dendritic cell maturation/functions.

Still, if we can use immunotherapy to overcome these evasion tactics, a pet’s immune system can play a valuable role in overcoming cancer. 

The Goal of Immunotherapy in Cancer 

When treating cancer with immunotherapy, the primary goal is to help the immune system develop an effective anti-tumor response. 

This immune response may occur slowly or rapidly, depending on the cancer and the type of treatment. Either way, the goal is that the immune system be able to effectively differentiate between normal cells and tumor cells, preferentially eliminating tumor cells. 

Types of Cancer Immunotherapy 

There are three primary types of cancer immunotherapy that are currently in development. Each type of immunotherapy uses a slightly different approach to optimize the immune response to tumor cells. 

• Adoptive Cell Therapy (ACT). In this treatment, cells are transferred into a patient with the goal of eradicating cancer. These cells may be the patient’s cells (which have been genetically modified or otherwise specially trained) or may be from another donor. For example, the University of Pennsylvania is currently conducting a study in which T cells are taken from the peripheral blood of a dog with cancer, genetically modified to recognize cancerous B cells, expanded to produce large numbers of tumor-specific cells, then injected back into the dog to combat B cell leukemia or B cell lymphoma.¹
  
  
• Systemic Immunomodulators. There are a number of types of immunomodulators that can be used in cancer therapy, including checkpoint inhibitors (which block checkpoints that are often established by tumors), agonists (which promote adaptive immune response), adjuvants (which stimulate general immune response), and cytokines (which regulate immune cells). Toceranib (Palladia^®) is a tyrosine kinase inhibitor that is used to treat mast cell tumors due to its immunomodulatory effects.² 
  
  
• Cancer Vaccines Against Tumor Antigens. Cancer vaccines train the immune system to recognize a specific tumor-associated protein, similar to the way that vaccines for infectious diseases train the immune system to recognize a specific protein associated with a virus or bacterium. Oncept^®, the canine melanoma vaccine, works according to this principle. 

The Future of Cancer Immunotherapy

The field of cancer immunotherapy is rapidly developing in both human and veterinary medicine. As new advances are introduced in the field of human oncology, we can expect that those treatments will continue to gradually filter over to veterinary medicine, becoming more widely available for veterinary patients. 

Cancer immunotherapy is a field that is rapidly changing and developing. As you graduate from vet school and head into your first job in practice, be sure to stay connected to news about veterinary oncology. Through continuing education, journals, and professional forums on social media, you can stay aware of new advances, allowing you to advocate for the best possible treatments for your patients. 

References

1. PennVet. Clinical Trials: Re-directed Autologous T cell Therapy for B cell lymphoma or B Cell Leukemia. 
2. Mitchell, L., Thamm, D. H., & Biller, B. J. (2012). Clinical and Immunomodulatory Effects of Toceranib Combined with Low-Dose Cyclophosphamide in Dogs with Cancer. Journal of Veterinary Internal Medicine, 26(2), 355–362.