Despite all the advancements in human medicine over the past few decades, veterinary medicine has seen little change until recently. Now, several new therapeutic developments have emerged specifically for use in veterinary medicine that have promising potential in changing how veterinarians treat cancer.
Cancer is a devastating disease for humans and the pets who are integral parts of their families. Cancer arises through accumulation of thousands of mutations, some of which generate drivers that lead to malignant transformation and cancer spread. Some of those mutations generate proteins that are recognized as foreign by the cancer-bearer’s immune system (cancer neoantigens). The growth and spread (metastasis) of a cancer involves complex interactions between cancer cells and normal host cells that populate the cancer tissue microenvironment. Some of those host cells suppress naturally occurring immune responses, which further promotes cancer growth and spread.
Recent advances in the fourth pillar of cancer treatment—immunotherapy—suggest that the immune system may be our best tool to cure more cancers. Various immune stimuli, including cancer vaccines and other biological response modifiers have been tested in dogs and humans with variable degrees of success. However, a notable challenge with these therapies is that while they will generate powerful immune responses against cancers, the effects of the immune cells—specifically T cells—that are generated from the stimulation and that infiltrate cancer tissue can be significantly suppressed by the cancer microenvironment. An example of these cancer defenses are checkpoint proteins on the surface of cancer cells. These checkpoint proteins identify cancer cells as “normal” cells and thus the immune system ignores them.
The capability of the immune system to kill cancer cells can be significantly boosted by removing T cells from the patient and converting them into effector T cells ex vivo , away from the immunosuppressive environment that exists within the patient’s body. One such approach that has had success in the treatment of leukemias and lymphomas is cellular immunotherapy with genetically engineered effector T cells called chimeric antigen receptor (CAR) T cells. Another that also has had considerable success in selected cancers is tumor infiltrating lymphocyte (TIL) therapy. Both CAR-T cell and TIL therapies have produced instances of cancer regressions and long-term patient survival when used to treat human patients with widespread metastatic disease.