Cancer is the most common cause of death in older dogs and cats. Despite this, there are several treatments available that can offer pets a good quality of life (QOL). Advances in veterinary oncology have increased owner awareness and the readiness of many veterinary practitioners to treat cancer patients. This means that greater numbers of pets with cancer are being managed long term. Cancer can potentially be a painful and debilitating disease, therefore those involved in the care of these patients should always consider the importance of treating the patient as a whole - not just medically, but in consideration of their overall QOL. From the outset of treatment, owners should be made aware that the goal of treatment in the majority of cases is to maintain optimum quality of life for their pet, as opposed to quantity.
The Concept of Quality of Life
In veterinary oncology, health-related quality of life (HRQOL) is often subjectively assessed and used as an outcome objective to make decisions regarding treatments and euthanasia of cancer-bearing patients and/or those undergoing cancer therapies. In human medicine, there is evidence that HRQOL can help to predict survival and it is thought that it could be used as an important predictor of survival in veterinary oncology patients. Further studies into this area of veterinary oncology are ongoing.
The goal of using HRQOL is to improve the subjective long-term outcome for the patient. Despite routinely using HRQOL as an outcome objective, few agreed criteria for its assessment and measurement exist, and it is frequently left to individuals; therefore the veterinary oncology field is currently attempting to develop standardised/universally accepted questionnaires to evaluate patient QOL. Ideally, only clinical signs causing distress or discomfort should be considered. However, as this is a subjective assessment, problems often arise due to variability amongst individuals, especially between veterinary professionals and owners. For example, signs noted by veterinary professionals, such as chemotherapy-related alopecia which are not causing a problem for the animal, may be perceived as an abnormality by the owner. Conversely, events (e.g., vomiting, diarrhoea), states of being (e.g., lethargy), decline or absence of normal functions (e.g., not urinating or defecating) or new conditions (e.g., new palpable masses) may not be perceived by the owner as a problem for the animal, but may be considered by veterinary professionals to negatively impact on QOL. Also, HRQOL is a dynamic concept and may change from day to day; or, the same clinical condition could result in diverse QOL issues in different patients or within the same patient at different times (with its assessment being influenced by owners' expectations and experience); or, pets whose health state has changed, may maintain a consistent level of HRQOL.
HRQOL of veterinary cancer patients is a multidimensional concept that encompasses both the physical (e.g., clinical signs caused by cancer, its affects and treatment) and social (e.g., effects of cancer on interaction with owners or other pets). Unfortunately, veterinary patients are incapable of giving first-hand information regarding their subjective experience and assessing HRQOL of animals must come indirectly from proxy informants - usually owners/family members.
HRQOL in veterinary cancer patients may be influenced and altered by multiple factors, which may include the tumour type, as well as the grade and stage, chosen treatment protocols and their adverse effects, the presence or absence of paraneoplastic syndromes, the patient's life stage and possible concurrent health problems and the patient's home/family circumstances.
Therapeutic Options
Aimed at maintenance of optimal QOL (with or without cure), the three most important treatment options used in veterinary oncology are surgery and/or radiotherapy and/ or chemotherapy.
Surgery may be diagnostic (collection of biopsy samples) or therapeutic (removal or debulking localised tumours).
Radiotherapy can be used alone or in conjunction with surgery and chemotherapy, to treat local or diffuse disease. Radiation may be used with palliative (analgesia for bone pain) or therapeutic intent. It is a specialist treatment, which may take the form of brachytherapy (e.g., iodine131 for hyperthyroidism in cats) or as electron or photon beams, delivered via a linear accelerator. It is most often used to treat smaller or debulked localised tumours.
Chemotherapy is used to treat systemic cancer and/or as an adjunct to surgery or radiation (to treat microscopic disease), or as neoadjuvant therapy (prior to surgery or radiotherapy).
All of these may impact HRQOL, ideally positively, but effects can be negative in the short (usually surgery), medium or long-term (radiotherapy +/- chemotherapy).
Chemotherapy
In human cancer therapy, chemotherapy is often very aggressive, with severe debilitating side effects, including immune suppression, vomiting and diarrhoea, weight loss and total hair loss. In veterinary oncology, as QOL is paramount, chemotherapy protocols are used which are less aggressive than those used for humans - in general the doses used are one-third of those used in human medicine, with lesser intensity, with the 'payback' often being limited life expectancy.
Combining cytotoxic drugs is an important, effective strategy in chemotherapy - when drugs are used in combination they often enhance the activities of each other, therefore minimising their dose-limiting toxicities.
Although serious adverse effects can occur, many do not require hospitalisation (~5%).
To ensure optimal QOL whilst undergoing chemotherapy, adequate time should be spent with owners to counsel them on what to expect during their pet's chemotherapy. When assessing HRQOL in conjunction with owners, beware - many perceive their pet's QOL to be worse, simply because it is on chemotherapy, even if it feels better!
Analgesia
Comfort management is central to maintaining good QOL and compassionate care requires that patients are kept as free as possible from the adverse effects that may be associated with cancer and its treatment. Whilst there have been few clinical studies into cancer pain in animals, it must be assumed - based on clinical experience, knowledge of other chronic pain states (e.g., osteoarthritis) and information extrapolated from human medicine - that veterinary cancer patients experience pain. Any tumour may cause pain. Pain can also be caused by related diagnostic procedures, pathological fractures, therapeutic surgical procedures, chemotherapy and radiotherapy (although considered palliative and pain relieving in themselves) and pre-existing chronic pain, such as arthritis. Pain should be managed by constant re-evaluation, tailoring of analgesic protocols to address patients' changing needs and being prepared to rethink/change the plan whenever appropriate, as well as multimodal pharmacological analgesia and excellent nursing, both at home and in the hospital.
Fear and stress, as well as learned patient expectation, should also be taken into account and managed, especially in view of the multiple/repeated treatment experiences these patients must undergo.
Nutrition
Meeting nutritional requirements is an important part of the care of cancer patients. Good nutrition has been shown in both people and in animals to improve not only QOL but also length of life by enhancing the beneficial effects of surgery, chemotherapy and radiation therapy, while at the same time reducing the side effects of these therapies. Whilst the ideal cancer diet for veterinary patients is not known, there are some general concepts which may be followed:
Provide a diet with an appetising aroma and taste.
Feed the patient appropriately for its particular clinical condition.
Minimise simple carbohydrates (starches and sugars). It is currently thought that dogs with certain malignant diseases may have changes in carbohydrate, protein and fat metabolism. Using foods low in soluble carbohydrate, but high in fat and protein of high biological value, may slow the metabolic changes associated with cancer.
Consider enhancing the levels of omega-3 fatty acids and arginine. Polyunsaturated omega-3 fatty acids may inhibit the growth and metastasis of certain tumours.
Consider the short- or long-term use of anti-nausea medication and/or appetite stimulants on a case-by-case basis.
When oral intake is not possible (e.g., following surgery or radiotherapy), assisted tube feeding is an option to enhance both QOL and longevity. The (temporary or permanent) placement of feeding tubes allows stress-free administration of medication, fluids and nutrition to patients either in the hospital setting or at home. Tube feeding should be instigated before significant weight loss / cachexia occurs.
When QOL is No Longer Attainable
With advances in veterinary medicine, decisions on when to let go have actually become more difficult than in the past, when all that could be done was to make a terminally ill pet as comfortable as possible for as long as possible. Now, many of the options of human medicine are available for pets, making it easy to persist with treatment when letting go is too difficult. When considering HRQOL, it should be remembered that, if a cure is not achievable, the increased level of care that can be offered to cancer-bearing pets is designed to prolong QOL, as well as quantity, but the former should take precedence.
In conclusion, from the initial presentation, diagnostic examinations and treatments, through to final decisions about euthanasia, the veterinary care team should not only provide for the medical and non-medical needs of the cancer patient and the client, but be aware of, and aspire to optimise, HRQOL whenever possible.