Beyond Chemotherapy: How Veterinary Oncologists Can Improve Outcomes and Extend Quality of Life
By: Angharad Waite VMD, DACVIM (Oncology)
The Oncology Service
As a veterinary oncologist, my primary objective is to provide information to my clients about the benefits and risks associated with a cancer treatment. A principal component of this effort is to bring hope to families and to provide prolonged high quality of life to my patients who have been stricken by cancer. The primary means to deliver the best care is through a personalized review of the available clinical information for a specific patient and a discussion about the cancer, its prognosis, and the spectrum of available treatment options. It is increasingly the case that this discussion does not focus on the use of chemotherapy alone.
A diagnosis of cancer is often obtained from a tissue section that has been submitted to a pathologist. The information provided on the pathology report can offer a wealth of information to the oncologist regarding the biologic behavior of that tumor type and what other diagnostic tests may be indicated to provide more prognostics information. Additionally, it is important to remember that the conclusions generated on the pathology report may not always be consistent with an oncologist’s experience or inclusive of the newest information available to an oncologist. With the development of advanced cellular and molecular tools, we are now able to extend the value of a pathology report and to provide additional information that is helpful and often essential to completely describe the prognosis for a given patient. This information can often provide insight into the necessity for and types of additional therapy that may be offered.
Once a diagnosis of cancer has been obtained, there are many treatment options. We are aware that chemotherapy is a term that carries many negative connotations for pet owners. The good news is that our ability to effectively manage the risks of chemotherapy have dramatically improved. Indeed, we can now be confident in a high level of quality of life for our patients. Nonetheless we understand that chemotherapy may not be in the interest of a family or may not be relevant to the treatment of a given cancer. Therefore, a concern about chemotherapy should not be the only basis to decide on the input of a cancer specialist. For example, if a primary bone tumor is diagnosed in the limb of a dog, surgery and chemotherapy would be one treatment option. However, if surgery and chemotherapy are not elected, many options remain.
Intravenous infusions of pamidronate, lidocaine and ketamine, and/or palliative radiation can markedly improve comfort and the ability to walk. Pamidronate is a bisphosphonate inhibitor which minimizes bone turnover (and therefore pain from the tumor destroying the bone) and is well tolerated. Palliative radiation is a short course of radiation treatment with reduced incidence of side effects and with the intent of improving comfort for the short term. In my experience, 60% of patients will respond to pamidronate and the improved comfort can be maintained for 2-6 weeks with treatments repeated as needed (often every other week). The reported response rate with pamidronate in the literature is 28-40% with pain control lasting for greater than 4 months. I have also routinely used lidocaine/ketamine infusions with pamidronate and have seen most patients show signs of improved comfort, typically within 24 hours, and this has lasted for several weeks before a repeat treatment is pursued. As such my role in improving outcomes, even in this single example, extend well beyond a focus on conventional chemotherapy.
Progress in the field has also taken us beyond chemotherapy alone. Advances in immunotherapy and targeted cancer therapy continue to be made in human and veterinary oncology. The two immunotherapies I most commonly use are inhaled IL-2 for lung metastases and the melanoma vaccine. IL-2 has a 30% response rate in patients with pulmonary metastatic osteosarcoma. This therapy has been well-tolerated in my patients and can result in stabilization and even regression of the metastatic lesions. The melanoma vaccine has shown significant improvements in survival time in dogs with malignant melanoma. Recently, a paper published looking at canine patients with oral malignant melanoma including dogs that had spread to local lymph nodes had long survival times when surgery and the vaccine were pursued. The median disease free interval was not reached at two years in these patients. In the future, additional novel immunotherapeutic drugs will become available and will be safely integrated into the care of our patients. In the setting of targeted therapy we are now in the era of targeted small molecule inhibitors for veterinary cancer patients. Two approved agents (Palladia and Masitinib) are available and more are expected for several cancers.
In summary my role as a veterinary oncologist extends well beyond that of chemotherapy. Changes in our field have increasingly required me to carefully review a pathological report and to consider what additional cellular and molecular tests are needed to fully define a diagnosis and prognosis. From there, my goal is to provide families with information on the specific cancer in their pet and discuss the diversity of options that can be used to treat cancer. This includes the use of chemotherapy combined with medications that successfully limit the side-effects previously seen with chemotherapy, and to include the vast numbers of new treatments from targeted radiation to immunotherapy and small molecule inhibitors into a treatment plan that meets the goals of each patient family.