Written by: Dr. Bob Rosenthal, Veterinary Oncologist
The word “chemotherapy” comes loaded with emotional baggage, and this itself is often a barrier for dog owners as they face decisions about treating their pets with cancer. Almost everyone has heard some bad stories about canine chemotherapy. As always, a bit of understanding and frank discussion about what’s really going on are helpful. These four facts about chemotherapy should help pet owners to understand what their veterinarian is proposing and, therefore, allow owners a more certain basis for important decision-making.
1) Chemotherapy simply means treatment with drugs. Common usage implies the use of cytotoxic drugs that damage cells. The intent is to kill cancer cells without damaging normal cells. With conventional chemotherapy, this means finding a balance between efficacy (killing the cancer cells) and toxicity (insulting the normal cells), a real challenge in many cases.
2) The balance between efficacy and toxicity sought in chemotherapy management is not unique to the medical part of the overall approach. It is also true for both surgery and radiation therapy that the proper “dose” of therapy is one that strikes a balance between efficacy and toxicity. Particularly in veterinary medicine, where no one will accept a treatment that is worse than the disease, the line will vary with each owner, patient, and treatment. The concern over adverse effects is not unique to chemotherapy; rather it is a principle that governs any therapy.
3) A different approach to treatment with drugs is called metronomic chemotherapy, also known as low-dose continuous or LDC chemotherapy. In conventional cytotoxic chemotherapy, the idea is to find the maximum tolerated dose and to treat repeatedly, as patient circumstances allow, trying to kill every cancer cell. With metronomic therapy, the idea is not really to kill cancer cells, but rather to deprive them of certain factors they need to grow and develop, and the blood supply they need to thrive. Metronomic therapy has found a place in veterinary medicine in the management of some carcinomas and sarcomas, usually as an adjunct to other therapy when there is concern about residual disease and/or metastatic potential. By and large, metronomic therapy is well tolerated with few side effects, but it is still important to monitor the patient closely.
4) Another relatively new approach to treatment with drugs is targeted therapy aimed at exploiting unique features or susceptibilities of cancer cells. For example, drugs that will inhibit the enzyme tyrosine kinase have been approved for use in mast cell tumors in dogs. Studies are underway to evaluate their use in other types of cancer, as well. While these drugs do offer a different approach, they are not without side effects and should not be used indiscriminately or without proper monitoring.
The most important thing a veterinarian can do when first discussing cancer with an owner is to provide the information that the owner needs to make a good decision about any aspect of the case (diagnosis as well as therapy), as each has an impact on prognosis. Of course, information is sometimes imperfect or, frankly, not available. It is on this front that the work of the Morris Animal Foundation, as supported by the Orvis Canine Cancer Campaign, is so important. There are newer horizons to be explored in the area of treatment of cancer with drugs, including many now being actively investigated with Morris Animal Foundation support. With better understanding will come better management and more quality time to share with our pets.