Section 2: What’s New in Veterinary Oncology

Tremendous growth has occurred in diagnostic and therapeutic offerings in veterinary oncology. Additionally, direct-to-consumer advertising has increased client awareness of these options, which clients then want to discuss with primary care veterinarians. Veterinarians must recognize that regulatory oversight of marketing for veterinary diagnostic tests and many treatments is limited. A wide range of scientific levels of evidence for reliability and efficacy of products exists. Careful review of peer-reviewed publications regarding new tests or therapeutics and weighing the potential costs versus proven benefits of any new offering is crucial. In addition, with new veterinary drugs, it is important to understand the FDA’s designation for drugs that have received conditional approval and how it affects the drug’s use (see Box: Key Points About Conditionally Approved Drugs). Some products, such as vaccines, are regulated by the USDA (see Box: USDA Regulation of Biologics). Staying informed on licensing and approval regulations ensures that veterinarians provide safe, effective cancer care while avoiding legal risks.

Diagnostics

Many veterinary cancer screening tests are marketed with the stated goals of helping detect and treat cancer early. Assessing the efficacy of such tests requires understanding positive and negative predictive values and how disease prevalence affects those values. At this time, no blood or urine test can conclusively rule in or rule out cancer in a veterinary patient, so these tests must be used with caution to avoid providing a false sense of security or causing undue alarm. Studies are ongoing for some of these tests, with the hope of identifying more precise and accurate ways to leverage them for the benefit of patients.

Two new types of tests have emerged that are intended to aid in cancer diagnosis and treatment:

• Liquid biopsy. These blood or urine tests detect substances that may be used as biomarkers and are intended to diagnose, screen for, or monitor cancer.
• Personalized/precision medicine profiles. These blood and tumor sample tests use various forms of biologic tumor profiling, which are intended to identify treatments that the tumor may be most susceptible to based on its genome rather than its histology (tumor type).

These are exciting developments; however, at this time, insufficient data exists to conclude whether these tests meaningfully improve outcomes in animals. General practitioners and specialists should be aware of the data and limitations of these tests before recommending or interpreting them.¹

Choose cancer diagnostic tests and methods wisely. In contrast to drugs, minimal to no regulatory approval process exists for veterinary cancer diagnostics and medical devices. Accordingly, a product’s presence in the marketplace does not establish that it has demonstrated accuracy or patient benefit.

Key Points About Conditionally Approved Drugs

Conditional approval is a regulatory pathway granted by the FDA for veterinary drugs that have demonstrated complete and acceptable safety and have a “reasonable expectation of effectiveness” when they are used according to the label.²

Under this designation, it is a violation of federal law to use these products in a manner other than what is specified on their label. Therefore, during the time a drug is sold under conditional approval, extralabel use is illegal. Extralabel is allowed only for drugs that are fully approved. Because more than 90% of drugs used in veterinary oncology are not approved in veterinary species and thus are used extralabel, the legal limitations in using conditionally approved drugs are often, and understandably, missed.

An FDA conditionally approved (CA) drug is noted by the drug’s trade name followed by CA and a number (DRUG NAME-CA1). For example, CA1 indicates that it is the first CA application for that drug, and CA2 indicates a second CA application for that drug. If a CA drug receives full FDA approval, the CA notation and number are no longer listed. During the conditional approval period, these drugs can be legally marketed and prescribed. This allows veterinarians earlier access to promising medications for conditions where fully approved alternatives do not exist. If the effectiveness standard for full approval is not shown within 5 years, the drug can no longer be sold.

USDA Regulation of Biologics

The USDA regulates biologics (e.g., vaccines, monoclonal antibodies) used in veterinary oncology, whereas the FDA oversees chemical-based drugs. USDA-licensed products, such as the Oncept canine melanoma vaccine and gilvetmab (anti-programmed cell death protein [PD-1] monoclonal antibody), are often restricted to specific indications and may be available only through specialists.

USDA-regulated biologics offer valuable options for hard-to-treat cancers, but their efficacy data may be less extensive. Veterinarians must critically assess available evidence and consult specialists as needed. Compliance involves adhering to label instructions and maintaining treatment records. These products enhance therapeutic choices but require careful consideration of their regulatory restrictions and clinical applications.

Newer Therapeutics

Systemic therapies

Rabacfosadine ^{3,4,5,6,7,8,9,10,11} is fully approved by the FDA to treat canine lymphoma. It is a double prodrug of a nucleotide analog that inhibits DNA synthesis by inhibiting DNA polymerases. The drug is administered as a 30-minute IV infusion, given once every 3 weeks for up to five doses. It is generally well tolerated, with gastrointestinal (GI) upset and neutropenia being the main side effects; cutaneous reactions and pulmonary fibrosis are less common but also of note. Publications describe its use in rescue therapy and naive lymphomas. It may also be combined in multidrug protocols. As it is a fully approved drug, extralabel use is permitted. In early studies, dogs with multiple myeloma showed strong therapeutic responses.¹²

Verdinexor ^13,14,15,16 is FDA conditionally approved to treat canine lymphoma. It is a selective inhibitor of nuclear export. It is given orally twice a week. Adverse reactions include anorexia, vomiting, diarrhea, and lethargy. In the initial approval study, all 58 dogs had at least one adverse reaction, and 36% of dogs had a severe or life-threatening reaction.¹⁷ Response rates are limited, and studies are ongoing for full FDA approval.

Crofelemer-CA1 is conditionally approved for managing chemotherapy-induced diarrhea in dogs.¹⁸ Crofelemer-CA1 is an oral antisecretory medication used to manage chemotherapy-induced diarrhea in dogs by regulating chloride and water secretion in the GI tract. It works locally in the gut and is minimally absorbed systemically.

Gilvetmab is a caninized monoclonal antibody against canine PD-1, which leads to a decrease in tumor-induced immune suppression and thus improves the immune system’s ability to destroy cancer cells.¹⁹ It is conditionally licensed by the USDA for use in dogs with mast cell tumors (MCTs) or melanomas and is available only through veterinary specialists practicing oncology. Studies are ongoing for full licensure.

Cell therapies (e.g., adoptive cell therapy, ELIAS cancer immunotherapy, and chimeric antigen receptor T-cell therapy) are another growing area for cancer treatment, and further research needs to be done. ^20,21,22

Autologous cancer vaccines (e.g., Torigen) represent a personalized immunotherapeutic approach by using a patient’s own tumor
tissue to stimulate an immune response. Although they are appealing because of their individualized nature and ease of administration, there remains limited peer-reviewed evidence supporting their efficacy in veterinary oncology. Further research is needed to better understand their clinical benefit, mechanisms of action, and potential role within a multimodal treatment plan.

Local therapies

Tigilanol tiglate ^23,24,25 is an FDA-approved local therapy for nonmetastatic canine MCTs. Cutaneous tumors anywhere on the body can be treated. To treat subcutaneous tumors, they must be located at or distal to the elbow or hock. Restrictions for use also exist for tumor size and total dose. Injection is restricted to intratumoral (avoiding the margins, periphery, and deep to the tumor) and leads to hemorrhagic necrosis of the tumor. Wound healing is usually complete within 4–8 weeks.

Electrochemotherapy ^{26,27,28,29,30,31} is another area of research and growth in local tumor treatment. A special unit generates an electrical field to increase cancer cell permeability, which can enhance chemotherapeutic efficacy.

The 2026 AAHA Oncology Guidelines for Dogs and Cats are generously supported by CareCredit, Hill’s Pet Nutrition, Merck Animal Health, and Zoetis.