by Veterinary Practice News Editors | May 6, 2009 11:24 am
While we have increasingly advanced therapies for treating canine and feline cancer, sometimes the most appropriate treatment is palliation.
Palliative therapy is defined as reducing or removing the symptoms of a disease or a disorder, not curing it. By this definition, the majority of veterinary cancer care falls under the umbrella of palliation.
While achieving a cure in most of our patients would be desirable, doing so at the expense of an animal’s quality of life contradicts the most basic principle of veterinary oncology. The most common comment I hear during oncology consultations is that clients do not want to extend an animal’s life at the expense of their quality of life.
I always tell my clients that while I don’t believe animals understand the concept of time, I think they understand quality of life and how they feel as they live in the present.
Though palliative treatment is often focused on relieving the pain of a tumor or cancer, or relieving the suffering caused by a tumor, pain isn’t necessarily the only reason for providing palliative care. Owners may not recognize that besides pain, there may be many other components to an animal’s suffering, such as respiratory distress, profound weakness or nausea.
The most important part of any consultation regarding a pet diagnosed with cancer involves educating the owner about the symptoms of that particular cancer, how to interpret an animal’s behavior in light of those symptoms, and how to anticipate and treat the signs of the disease before they occur.
The mainstay of cancer pain control is non-steroidal anti-inflammatory drugs, or NSAIDs.
Historically, the most noteworthy NSAID used to treat tumors has been piroxicam, a nonspecific cycoloxygenase (COX) inhibitor with proven efficacy in the treatment of canine oral squamous cell carcinomas and canine transitional cell carcinomas. While investigations into the anti-tumor properties of other more COX-specific NSAIDs are ongoing, no other NSAID has been proven as efficacious for tumor control as piroxicam.
However, most veterinary NSAIDs are excellent choices for tumor-associated analgesia. For extremely painful tumors, such as osteosarcoma and other bone tumors, NSAIDs alone are unlikely to provide adequate analgesia and are often combined with tramadol or gabapentin and other modalities.
Steroids play a major role in cancer palliation. Most commonly they are used in the palliative treatment of canine and feline lymphoma and canine and feline mast cell tumors. Not only do they provide immediate relief of peri-tumor edema and inflammation, but they have direct lytic effects on both lymphoblasts and mast cells.
Any time one is providing palliative care to a cancer patient, a frank conversation of expectations and goals must be had with the owner before embarking on any therapy.
Additionally, steroids act as a calcinuretic and may be used as adjunctive treatment or the sole palliative treatment to reduce serum calcium levels associated with neoplasia. Bisphosphonates, which have anti-osteoclastic activity, can be indispensable in both lowering serum calcium and reducing the pain of bony tumors.
Controlled drugs, like opioids, also have a place, albeit a small one, in cancer palliation. While the short-term pain relief they can provide can be irreplaceable, there is little use for opioids in a long-term setting. Once an animal’s pain is responsive only to opiods, a frank conversation about the animal’s quality of life and euthanasia should be had with the owner. For example, I tend to discourage the use of fentanyl patches or limit the patient to one depending on the specific situation.
While pain medication is of primary importance when treating any animal with a possibly painful tumor, there are clinical signs other than pain, such as weakness and dyspnea, that may be just as distressing to an animal.
Chemotherapy and radiation therapy are often used when a cure is not possible, but adequate palliation may be. Animals with neoplastic effusions may be palliated with intracavitary chemotherapy. Carboplatin and cisplatin are the mainstays of intracavitary chemotherapy.
While cisplatin may have a deeper penetration into serosal neoplastic implantations, it has often been replaced by less-nephrotoxic carboplatin. For example, an animal with intrathoracic carcinomatosis and pleural effusion may be treated with serial thoracocentesis and intrathoracic instillation of chemotherapy. Additionally, blood transfusions can be instrumental in combating anemia-associated fatigue and may be given palliatively to an animal with an end-stage bleeding tumor.
Animals who are still clinically well but have monitorable evidence of tumor or metastasis may be given chemotherapy to stabilize or slow the growth rate of the metastatic lesions. Repeated monitoring and staging is crucial for continuing therapy and should be performed at every one to two doses. Tumor selection is essential as some tumors (a rapidly-growing carcinoma, for example) may be more responsive than others (such as a slow-growing sarcoma).
Consultation with or referral to an oncologist may be the best approach for devising a plan for treating these cases.
External beam radiation therapy also has a place in the palliative care of many tumors. The most common form of radiation therapy is definitive intent, or full course. It is used on incompletely resected tumors where microscopic disease remains. But indications for palliative radiation therapy in veterinary oncology are numerous.
They include non-surgical osteosarcomas, large and unresectable soft tissue sarcomas and unresectable mast cell tumors.
Radiation schemes for these types of tumors often involve coarse fractionation (usually one treatment weekly), which can provide short-term relief of the clinical signs of the tumor including pain, discharge and swelling, with the added benefit of less acute toxicity than definitive radiation and less cost to the owner.
Late-term toxicity would be a consequence of this treatment, and therefore careful patient selection and owner education are of utmost importance when considering palliative radiation.
Any time one is providing palliative care to a cancer patient, a frank conversation of expectations and goals must be had with the owner before embarking on any therapy. Similar conversations should take place periodically throughout treatment.
For instance, it may not be appropriate for an animal to have serial frequent thoracocenteses if that patient is not responding to chemotherapy. It also is wise to be frank about how many transfusions are to be offered in a dog with a recurrent metastatic non-surgical hemangiosarcoma. At the outset, the doctor should clearly explain the criteria for continued treatment.
These decisions on limitations have important ethical and humane implications. Exactly how to address these issues with pet owners may vary highly depending on the practitioner.
Many owners seek complementary or alternative medical care once their animal has been diagnosed with cancer. While a discussion of alternative therapies is out of the scope of this article, the palliative benefits of some of these therapies, such as acupuncture in an arthritic patient with non-surgical osteosarcoma, should not be ignored.
As more advances are made in veterinary oncology, nothing will ever surpass the importance of the palliative treatment of our patients. Multimodal therapies combining pain control, radiation and chemotherapy can be used to provide comfort and ease suffering of patients even in the most advanced stages of their disease.
Karen Oberthaler, VMD, Dipl. ACVIM (Oncology), is a medical oncologist at NYC Veterinary Specialists and Cancer Treatment Center.
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