A cancer diagnosis is always difficult. Traditionally, we have several treatment options including surgery, chemotherapy, and radiation, or sometimes a combination of these modalities. Immunotherapy adds a fourth tool to our treatment tool box. While immunotherapy treatments are more commonplace in the fight against cancers in people, more options are becoming available to our veterinary patients.
The U.S. Department of Agriculture, which licenses veterinary vaccines and biologics, has now approved or conditionally approved three immunotherapies for dogs: one labeled for oral melanoma, one labeled for mast cell tumors and melanoma, and one for osteosarcoma, the most common primary bone tumor in dogs. Each works differently, and each has limits worth knowing before you ask your vet about it.
How does immunotherapy differ from traditional chemotherapy?
Chemotherapy kills any rapidly dividing cells such as cancer cells, but is not cancer specific. It may also impact the cells of the GI tract or the bone marrow, which are cells that turn over more rapidly than other tissues. In contrast, immunotherapy harnesses the body’s own immune system to help fight cancer cells.
Cancer can survive in the body by hiding from the immune system. Tumor cells look enough like normal cells that the immune system ignores them, and many tumors send out signals that switch off the T-cells sent to attack them. Immunotherapies work by making cancer cells more “visible” to the patient’s own immune system. For example, the Oncept melanoma vaccine, teaches the immune system to see a specific protein expressed by melanocytes, the cell of origin in melanoma. Others, like gilvetmab, block the “off switch” the tumor uses to block T-cells that interact with the tumor, allowing them to attack. The ELIAS treatment does both: it vaccinates the dog against its own tumor, then harvests the resulting T cells, activates them in a lab, and puts them back to fight tumor cells in the body.
Below are more in depth descriptions of the current commercially available immunotherapies for dogs:
Oncept melanoma vaccine, is the oldest of the three currently available immunotherapies. It is labeled for dogs with stage II or III melanoma of the mouth after surgery or radiation has removed the visible tumor, although it’s used commonly for melanoma on other parts of the body as well.
Oral melanoma is a highly aggressive cancer with a 50-80% rate of spread even after the tumor is removed. Melanoma cells make a protein called tyrosinase, but so do normal melanocytes, so a dog’s immune system won’t go after these cells. Oncept delivers the human gene for tyrosinase instead. Human tyrosinase is roughly 90% identical to the dog version: different enough to hopefully provoke an immune response, but similar enough that it “tricks” the immune system into attacking residual melanoma cells that may be left circulating around the body following surgery and/or radiation.
The vaccine is given as an initial booster series with 4 doses given two weeks apart, then a booster every six months. Side effects are rare and mild. The honest caveat is that the survival data are mixed. Early studies showed dogs living well past historical controls, but later retrospective reviews found smaller or no survival differences; however, these newer studies have lower stage tumors than previous studies. Larger, more prospective controlled studies are likely needed. Many oncologists still recommend it because the downside is low and we do not have many other convincing treatment options to help delay or prevent tumor spread.
Gilvetmab is the first checkpoint inhibitor for dogs. If you’ve heard of Keytruda, the human cancer drug, gilvetmab is the version geared towards dogs. This is a “caninized” antibody that blocks PD-1, a receptor on T-cells that tumors exploit to shut down the immune response.
USDA has conditionally licensed it for dogs with stage I to III mast cell tumors and stage II to III melanoma. “Conditional” means the manufacturer, Merck, has shown safety and a reasonable expectation of efficacy, but the full evidence package isn’t done. It’s given as a 30-minute IV infusion after a dose of diphenhydramine every 2 weeks for up to 10 doses.
The first peer-reviewed results came out in October 2026 in the Journal of Veterinary Internal Medicine. Across melanoma and mast cell tumor patients, approximately 65 percent saw their disease shrink or hold steady. Forty-six percent of dogs with mast cell tumors had tumors shrink, and the median time to progression hadn’t been reached when the study closed. Melanoma was tougher, with 20 percent responding and another 40 percent stable. Serious side effects hit ~6% of dogs; the common ones were tiredness, poor appetite, and vomiting.
ELIAS Cancer Immunotherapy (ECI) is a personalized treatment for osteosarcoma in dogs. Osteosarcoma most commonly occurs in the limbs of medium to large breed dogs, although any breed can be affected. Current standard treatment is amputation of the impacted limb followed by carboplatin chemotherapy. Unfortunately, despite aggressive treatment, most dogs will succumb to this disease within a year of diagnosis. ELIAS Cancer Immunotherapy, or ECI, is the first product USDA has approved treatment of osteosarcoma. Full approval came in March of 2025.
ECI is made specifically for each patient. The decision to pursue this treatment has to come before surgery, because ELIAS needs a piece of the tumor to create an autologous tumor vaccine. The vaccine is then injected intradermally 3 weeks in a row near draining lymph nodes to alert the immune system to the cancer antigen. Following the vaccine series, the patient undergoes apheresis, where blood runs through a machine that pulls out the T -cells now primed against the tumor. ELIAS activates those cells in its lab and ships them back for an IV infusion. Finally, the patient received a series of subcutaneous IL-2 injections commonly given by the owner at home to help keep the T-cells alive in the patient.
The survival data are early but encouraging. In an ongoing study of ECI given after a single dose of carboplatin chemotherapy, 71 percent of dogs were alive at one year, which is longer than the outcome for amputation and chemo alone, which had a one-year survival rate of 26%. Friendship Hospital for Animals is the only hospital on the East coast where this therapy can be performed under one roof.
Take-home message
While cancer immunotherapy is an exciting and promising field, we are still learning about it and how best to use it in our veterinary patients. If your pet receives a diagnosis of cancer, your oncologist will talk about all treatment options available and whether immunotherapy makes sense as part of the therapeutic plan. Currently, immunotherapy does not replace standard treatments of surgery, radiation, and chemotherapy; however, it can be a valuable tool for certain cancers. The research continues to grow and we’re hopeful to have even more of these therapies available to us in the future.
For more information or to set up a consultation with Friendship’s Oncology Department visit our Oncology page here.
Dr. Amanda Foskett is a Diplomate of the American College of Veterinary Internal Medicine (Oncology). She graduated from Duke University, where she double-majored in French studies and Biology with a focus in marine biology. She attended veterinary school at the University of Florida before completing a 1-year rotating internship at Friendship, followed by a 3-year medical oncology residency program with The Oncology Service.
