Merck Animal Health’s Esther Chon, DVM, DACVIM, Board Certified in Oncology, delivered “Updates on Immunotherapy,” as the last summer webinar in ACCC’s annual “How to Navigate through the Cancer Diagnosis” series for primary care veterinarians. A recording of her presentation is available HERE. Merck Animal Health has sponsored the summer series for the past three years.
Dr. Chon’s talk focused on the promise of immunotherapy as the new fourth pillar of treatment options in the fight against cancer in pets. In addition to the traditional protocols of surgery, chemotherapy, and radiation, immunotherapy offers new hope, thanks to promising immune checkpoint inhibitors, including Merck Animal Health’s gilvetmab.
Dr. Chon said that human cancer treatment has been revolutionized during the last decade thanks to immunotherapy. Finally, pets are now able to benefit from this treatment option that harnesses the body’s own immune system to eradicate cancer cells.
“Cancer evades the immune system,” she said. “Immunotherapy, which can also work synergistically with other therapies, uses the body’s own defenses to attack cancer cells.”
She reviewed in detail the various types of immunotherapies currently available to treat cancer in animals and the science behind the checkpoint inhibitor approach in teaching cells of the immune system to identify and help destroy cancer cells.
“Checkpoint inhibitors are monoclonal antibodies that help T-cells to fight cancer,” explained Dr. Chon. “The antibodies do not target the cancer specifically, rather they prevent the cancer from turning off the immune system.”
Gilvetmab, which is a “caninized anti-PD-1 monoclonal antibody that has received conditional approval for the treatment of dogs with stage I, II, or III mast cell tumor or stage II or III melanoma,” is the first commercially available immune checkpoint inhibitor in veterinary medicine. It is conditionally licensed by the USDA after showing “preliminary safety and efficacy in dogs with mast cell tumor or melanoma.”
According to Dr. Chon, in an initial trial of 26 dogs with mast cell tumors, 73% experienced “a decrease in target lesion size or maintenance of stable disease.” Of the 25 dogs with melanoma, 60% experienced “a decrease in target lesion size or maintenance of stable disease.” All participating dogs were client-owned.
The treatment is administered intravenously over a 30-minute session and few side effects have been reported. She emphasized that while gilvetmab has demonstrated a reasonable expectation of efficacy as a monotherapy, no single cancer therapy works perfectly alone, and immunotherapy is no exception. Often, other concurrent therapies, such as radiation therapy or chemotherapy, could in fact help boost the ability of the immune checkpoint inhibitors to recognize the tumor as the “enemy.” However, there is currently no evidence to support the use of concurrent cancer therapies with gilvetmab, although studies evaluating the safety and efficacy of gilvetmab used concurrent with other cancer therapies are ongoing.
One challenge, she pointed out, is the occurrence of “pseudoprogression,” where the tumor sometimes enlarges before it shrinks. An uncommon incident in human cases, this phenomenon can be the result of the immune cells infiltrating the tumor and causing the tumor to increase in size. Although such a development can cause alarm in pet owners, it could be a positive sign. When pseudoprogression is suspected, Dr. Chon recommends contacting your oncologist and Merck Animal Health’s pharmacovigilance team to discuss next steps. To differentiate pseudoprogression from true progression as the underlying cause of tumor enlargement, a biopsy is ultimately necessary.
She stressed the importance of consulting with a trained oncologist prior to any therapy, including surgery, to determine if immunotherapy is the best treatment. The earlier the referral to an oncologist, the better in being able to provide a more informed prognosis and therapeutic plan for the patient.
Clinical trials using immunotherapy currently are being held across the country. For more information about gilvetamb, click HERE.
