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Find information on animal health topics, written for the veterinary professional.

Drugs Used to Treat Cancers and Tumors

By Philip T. Reeves, BVSc (Hons), PhD, FANZCVS, Chief Regulatory Scientist, Veterinary Medicines and Nanotechnology, Australian Pesticides and Veterinary Medicines Authority
Dawn Merton Boothe, DVM, PhD, Professor, Department of Anatomy, Physiology, and Pharmacology, College of Veterinary Medicine, Auburn University
Maya M. Scott, BS, DVM, Resident, Clinical Pharmacology, Department of Veterinary Physiology and Pharmacology, College of Veterinary Medicine, Texas A&M University
Ian Tizard, BVMS, PhD, DACVM, University Distinguished Professor of Immunology; Director, Richard M. Schubot Exotic Bird Health Center, Department of Veterinary Pathobiology, College of Veterinary Medicine and Biomedical Sciences, Texas A&M University
Jozef Vercruysse, DVM, Professor, Faculty of Veterinary Medicine, Ghent University
Jörg M. Steiner, DrMedVet, PhD, DACVIM, DECVIM-CA, AGAF, Associate Professor and Director, Gastrointestinal Laboratory, Department of Small Animal Clinical Sciences, College of Veterinary Medicine and Biomedical Sciences, Texas A & M University

Antineoplastic (antitumor) chemotherapy is often used to treat dogs and cats, and it is routinely used for selected tumors in horses. Antineoplastic drugs can be grouped into general categories, based on their biochemical method of action: alkylating agents, antimetabolites, mitotic inhibitors, antineoplastic antibiotics, hormonal agents, and other miscellaneous drugs.

Chemotherapy drugs are usually given in various combinations of dosages and timing, which are referred to as regimens or protocols. This offers many advantages, because when drugs with different targets or mechanisms of actions are combined, the chances for success are greater.

Chemotherapy may be used in addition to surgery and radiation. Sometimes chemotherapy is started before surgery in an attempt to decrease tumor size or stage of malignancy, thus improving the chances of successful surgery.

The decision to use chemotherapy depends on the type of tumor to be treated, the stage of malignancy, the condition of the animal, and financial constraints. Responses to cancer chemotherapy can range from a decrease in day-to-day signs but no overall increased survival time to a complete remission. Some tumors respond better to chemotherapy than others. For example, canine lymphoma is usually very responsive to chemotherapy. You should discuss the options and the risks and benefits of each with your veterinarian if you are considering chemotherapy to treat cancer in your pet.