By Barbara Biller, DVM, PhD
Vet Clin Small Anim 44(2014) 817-829
Most of us have had a loved one stricken by cancer and, thus, we are familiar with the conventional cancer chemotherapeutic approach. Traditionally, a cancer patient is treated with a high dose of a drug, or drug combination, that is more toxic to rapidly dividing cancer cells than to normal tissues. The patient typically suffers side effects such as nausea, hair loss and fewer red blood cells. The treatment is followed by a break to allow drug-sensitive normal tissues to recover. Then the treatment is repeated. This conventional chemotherapy has led to improved survival for many cancer patients, but it often fails.
Dr. Barbara Biller is a veterinary oncologist at the Flint Animal Cancer Center, affiliated with Colorado State University. Her research, funded in part by the AKC Canine Health Foundation, is testing a new approach to cancer chemotherapy, called metronomic chemotherapy. A metronome is a device that produces a regular tick, tick, tick that musicians use to keep a steady tempo. Metronomic chemotherapy is the daily administration of a low dose of the same toxic drugs as conventional chemotherapy. This low dose doesn’t kill the tumor cells, but there is evidence it does prevent the growth of blood vessels into the tumor. Starved of nutrients, the tumor dies. The metronomic dose also appears to “wake up” the immune system, leading to an antitumor immune response.
Metronomic chemotherapy has been tested in several human clinical trials with patients who had advanced cancer that had failed to respond to conventional chemotherapy. Dr. Biller reports that, despite promising results, metronomic chemotherapy is still considered investigational and is not offered as a first-line therapy.
Dr. Biller cites nine published clinical trials of metronomic chemotherapy in dogs and cats. The treatment is easy to administer, reasonably priced and well tolerated. There is early evidence of overall clinical benefit. Dr. Biller states, “Although metronomic chemotherapy is an attractive treatment choice, it is still considered an experimental approach with the potential for toxicity. When available, conventional therapies should first be offered before turning to a metronomic protocol. Because stable disease is generally the goal of therapy, it is also important to consider the overall condition of the patient; living with stable disease should be expected to result in an acceptable quality of life. When used appropriately, there is much potential for metronomic chemotherapy to improve, not just maintain, quality of life for companion animals with cancer, especially as additional studies answer important questions regarding indications, drug dosages and patient monitoring.”