The four pillars of cancer treatment include surgery, chemotherapy, radiation therapy and immunotherapy. Veterinary oncology has largely relied on surgery, chemotherapy and radiation therapy - alone or in combination - to shrink or remove tumors and destroy cancer cells for years. While immunotherapy has transformed the landscape and been used in human oncology for some time, it is a relatively newer consideration for treating certain cancers in our veterinary patients.
Understanding Immunotherapy.
All animals - human and non-human alike - have sophisticated immune systems designed to fend off foreign invaders or pathogens - anything that it recognizes as an antigen or non-self. T cells are one important component of the immune system and are integral to the destruction of antigens - whether due to an infection, growth of tumor cells, etc. While the normal immune system is designed to recognize and destroy these threats, it also has regulatory pathways or “off switches” to prevent ongoing or excessive damage to adjacent normal tissues or regions of the body.
Cancer is technically a "foreign invader" but, unlike some of the more common pathogens like bacteria and fungi that are effectively identified and destroyed by our immune system, tumor cells have evolved in ways to avoid being picked off by the immune system. Cancer cells have essentially "learned" to exploit those "off switches" / regulatory pathways and essentially hide from T cells. Effectively, tumor cells are equipped to hide from the immune system.
Disrupting Tumors with Immune Checkpoint Inhibitors.
Monoclonal antibodies are a type of immune checkpoint inhibitor and, when used in the treatment of cancer, essentially block the "off switches" on tumor cells, thus allowing T cells to destroy them. In human oncology, there are many of these antibodies that are approved for use to treat a variety of different cancers.
Immune checkpoint inhibitors only recently made their way into the world of veterinary cancer care (in or around 2023). The first USDA conditionally approved product to come to market - gilvetmab - is a canine-specific, monoclonal antibody therapy that is available for use by veterinary oncologists for the treatment of canine mast cell tumors and melanoma. In clinical trials, this drug had a strong safety profile and was shown to be effective with 40% of dogs with mast cell tumors experiencing tumor shrinkage and approximately 20% of dogs with melanoma responding.
One challenge with this form of therapy is identifying the patients who might benefit and respond to treatment. In human oncology, biomarkers have been identified to help refine patient selection and predict response to therapy, however this is still an area of needed research in veterinary medicine.
In this excerpt from our webinar on Treating Cancer - Beyond Chemotherapy and Radiation - Dr. Doug Thamm - a veterinary oncologist at Colorado State University's College of Veterinary Medicine - shares some insights into immune checkpoint inhibitors, gilvetmab, and some of the ongoing challenges:
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