Treating cancer pain in dogs and cats
Pain frequently accompanies cancer in people and is also common in cancer-bearing dogs and cats. Pain negatively affects quality of life and important physiological functions, and eliminating it should be a priority. Whether cancer pain has been identified, is suspected, or is expected to occur in a cancer-bearing patient, efforts should be directed at treating and preventing it effectively. While pain in certain dogs and cats with cancer will be relieved with treatment directed toward the underlying cancer, others will require symptomatic analgesic therapy to improve their quality of life. A relative abundance of literature discusses the management of cancer pain in people.1-7 In contrast, there is a paucity of information specifically regarding the management of veterinary cancer pain. Recent publications, ongoing prospective studies, and better knowledge of the available therapeutic options should provide the necessary framework for appropriate pain management in cancer-bearing pets.8-14
METHODS OF PAIN RELIEF FOR CANCER PATIENTS
The most rational way to alleviate cancer pain, whenever possible, is to treat the underlying tumor. Always evaluate the possibility of surgically removing a resectable tumor or obtaining a remission by using radiation therapy for a radiosensitive tumor or chemotherapy for a chemosensitive cancer. While you are waiting for the definitive therapy to take effect and eliminate the source of pain, analgesic and supportive therapies are often required to improve a patient's quality of life. And occasionally, with resistant, refractory, recurring, or terminal cancers, only palliative therapy can truly benefit a patient.The goal in managing dogs and cats with cancer is to control pain and improve a patient's overall quality of life by using traditional anticancer therapeutic modalities, various analgesic therapies, and supportive care. Before you treat for cancer pain, you must have a basic understanding of the pathophysiology of pain and of the methods used to recognize and evaluate pain in veterinary patients (see the article "Understanding and recognizing cancer pain in dogs and cats").
TREATMENT DIRECTED AT THE TUMOR
Whenever possible, completely remove a painful tumor surgically. With an appropriate preemptive and multimodal analgesic program in place, including postoperative pain management, most patients with tumors causing pain will be more comfortable after radical surgeries. Surgery is the modality that can most rapidly eliminate the source of pain, and various surgical procedures can be performed, depending on the tumor's type, extent, and location. Examples of tumors best treated and possibly cured with surgery alone include canine oral tumors such as squamous cell carcinoma and fibrosarcoma, cutaneous mast cell tumors, mammary tumors, soft tissue sarcomas, splenic or hepatic tumors with painful capsular distention, nail bed tumors, synovial cell sarcoma causing bone lysis, and tumors of the ear canal.
Occasionally, patients will benefit from palliative surgeries to remove painful tumors, although the surgery itself may not positively affect the overall prognosis for survival. A classic example is a painful appendicular osteosarcoma in which metastatic disease ultimately determines the survival time. In this example, amputating the limb provides immediate relief to the patient, and adjuvant chemotherapy is administered to prolong survival and delay the growth of micrometastatic disease.
Surgically removing pulmonary metastatic lesions to provide relief from painful paraneoplastic hypertrophic osteopathy has been described. In a recent study in four dogs with osteosarcoma, pain relief from hypertrophic osteopathy was observed in all dogs less than 24 hours after metastasectomy.15 Peripheral and central neuroablative surgeries can be contemplated in select cases; these surgeries have proved valuable in people with terminal cancer and poorly responsive pain. Such salvage analgesic techniques are relatively novel and have yet to be described for the control of veterinary cancer pain.1-3