Palliative Care and the Veterinary Patient
PALLIATIVE CARE AND THE CANCER PATIENT
Craig A Clifford DVM, MS, DACVIM (Oncology)
Hope Veterinary Specialists
40 Three Tun Road
Malvern, PA 19355 USA
Palliative care is defined as treatment of symptoms of a condition, rather than treatment of the underlying condition itself. The world health organization defines palliative care as "The active total care of patients whose disease is not responsive to curative treatment. Control of pain, of other symptoms, and of psychological, social and spiritual problems, is paramount. The goal of palliative care is an achievement of the best quality of life for patients and their families”. is believed that ~ half of all animals with cancer will die as a result of the disease and most will require symptom or pain control. The need for palliative care in veterinary oncology is already great but will likely continue to increase over time.
Pain is a primary concern of most owners upon hearing the diagnosis of cancer and their feeling of not wanting their pet to be considered ”in pain”. Pain is a normal physiologic response that typically serves a protective function; however, pathologic pain results from overt damage to nerves or tissues. Tumors are generally poorly innervated structures but may induce pain via by the pressure on normal tissue and their subsequent destruction. Primary treatment of the tumor may result in some degree of pain control even if the tumor does not respond by a reduction in volume. The analgesic effectiveness of radiation therapy is well documented in the treatment of bone pain, metastases, and cancer of the central nervous system. The effect of chemotherapy on cancer pain is generally associated with a reduction in tumor size. Surgery can relieve pain and discomfort via removal or an ulcerated superficial mass, large oral tumors preventing adequate nutrition, gastrointestinal obstruction, abscessed tumor, compression of nervous tissue by a tumor etc. The benefits of this type of therapy need to be adequately weighed against the risks such as the associated hospitalization time, recovery time and the overall expected duration of benefit.
Although data is limited, acupuncture, chiropractic management, and physical therapy may be incorporated into pharmacologic management of pain to enhance overall well-being.
Palliation as a Primary Therapy:
Primary therapy for palliative purposes is accomplished in order to control symptoms associated with cancers includes physical disruption of vegetative functions such as dysphasia, tenesmus, dysuria and, dyspnea and symptoms associated with metabolic or paraneoplastic sequelae to cancer such as anemia, cachexia, hypoglycemia or hypercalcemia.
Surgery may be beneficial if the symptoms are associated with the presence of a mass and ideally reducing the mass will improve those symptoms. The goals of primary therapy in a palliative setting are certainly different than in a curative setting and these need to be addressed with the owner to manage expectations. Palliative surgical debulking is not intended to include large normal tissue margins but simply remove enough of the tumor to alleviate symptoms. Cases in which a tumor is large enough to affect nutritional intact, urination or defecation, respiration ambulation or may be infected are all examples in which a debulking may provide a benefit.
We often break radiation therapy into one of two categories based on the total radiation dose and fractionation scheme:
Definitive (curative intent) radiation protocols typically entail the delivery of 2.25 to 3.20 Gy/fraction on a M-F schedule for a total of 16 to 25 treatments resulting in a total dose of 48 to 63Gy. Generally, this is reserved for the microscopic setting.
Palliative (hypofractionated) radiation protocols typically involve the administration of a larger dose per fraction, with fewer total fractions and lower total radiation dose. On the positive side, in regard to quality of life, palliative protocols typically are associated with little to no acute adverse effects seen with definitive protocols such as moist desquamation of the skin or oral mucositis. The larger dose/fraction, however, is associated with an increased risk of late adverse effects, but ideally, most animals receiving palliative radiation therapy typically will not live long enough to develop late effects. Palliative radiation therapy is used in the treatment of canine appendicular osteosarcoma, oral tumors, nasal tumors, hemangiosarcoma (SQ/IM), thyroid carcinomas, mast cell tumor, injection site sarcoma, and soft tissue sarcomas. A variety of palliative protocols exist and these include:
8 Gy/fraction, given once weekly for 4 consecutive weeks for a total dose of 32 Gy.
5 Gy/fraction once daily for 5 consecutive days for a total dose of 20 Gy.
Sterotactic radiation therapy is also considered hypofractionated delivery extremely high doses/fraction in 1-3 treatments. It is sometimes called radiosurgery, and an example is CyberKnife. CyberKnife utilizes hundreds to thousands of small beams of radiation to target a tumor, which is administered from up to 1200 different angles around a patient’s body, thus “painting” on a dose of radiation with submillimeter accuracy. This means that a clinically insignificant dose of radiation is received by the healthy tissue surrounding a tumor, making radiation side effects minimal to absent. CyberKnife is able to deliver a very large dose of radiation in 1-3 treatments, which is equivalent to 3-4 weeks of daily treatments on a conventional linear accelerator. This results in a patient being required to undergo anesthesia fewer times and completion of a radiation protocol in one week or less.
Chemotherapy, when used in a palliative setting, is administered to attempt reduction or stabilization of the tumor to improve quality of life. One could say treatment of any bulky tumor would be described as “Palliative” in nature, however, for the purposes of this lecture, we reserving this for patients whose cancer has adversely affected their quality of life. Responses to chemotherapy in such a setting have been noted with transitional cell carcinoma, hemangiosarcoma, soft tissue sarcoma, mast cell tumor, histiocytic sarcoma, thyroid carcinoma, etc.
The use of expandable stents for relieving luminal obstruction secondary to cancer can be performed under fluoroscopic guidance, and have been evaluated in patients with urethral and colonic neoplasia. In select cases, this may actually be a life-saving procedure.
Malnutrition can occur as a result of cancer and it has been shown that while ~ 4% of dogs with cancer were emaciated (defined as body conditioning score < 3 out of 9) at the time of initial diagnosis, 68% had documented evidence of weight loss and 15% had moderate to severe muscle wasting. Cancer Cachexia is defined as a metabolic alteration and weight loss despite adequate nutrition. This is not to be confused with Cancer Anorexia which is weight loss and metabolic alterations associated with inadequate nutrition. Cancer cachexia is a real entity and likely underestimated in veterinary medicine. The incidence is likely higher in cats vs. dogs. The cause is unknown, however, metabolic alterations in carbohydrate, protein and lipid metabolism occur as a result of cancer. Cancer cells prefer anaerobic glycolysis which results in hyperlactatemia. The conversion of lactate to glucose (Cori cycle) yields a net energy loss. A negative nitrogen balance can also lead to immunosuppression.
There are three associated phases of cachexia:
1. Silent phase: No clinical signs of the disease are present, however, biochemical changes such as hyperlactatemia,
hyperinsulinemia, and alterations in amino acid and lipid profiles are noted.
2. Clinical Phase: At this point, patients will demonstrate signs such as anorexia, lethargy and weight loss.
3. Severe Phase: This phase is associated with weakness, severe debilitation, and significant weight loss.
A patient's nutritional assessment is based on both a thorough history (type of food, number of meals, how voracious a patient is in eating) and physical examination (assess body weight, body condition score, and overall muscle mass). The extent of nutritional support is based upon the results of the history and exam. Often is may require on mild intervention such as introducing higher coloric diets or medications such as appetite stimulants (megesterol acetate, prednisone, cyproheptadine, and mirtazapine), antiemetics (metoclopramide, dolasetron, ondansetron, and maropitant) or gastrooprotectants (famotidine, sucralfate, and omeprazole). For some, there is an ethical dilemma in the placement of feedings whether nasogastric, gastric or intestinal for palliation. In rare cases, in which a bulky mass prevented the ability to ingest adequate nutrition, I have used more aggressive means to ensure adequate nutritional intake but this represents a minority of cases.
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