The goal of cancer treatment in the veterinary patient is to prolong good quality of life for as long as possible. Quantity of life is meaningless without quality. Because quality issues are vague and changeable, it is easy to focus instead on quantity because that is a specific, well-defined goal. It is important to keep these two factors in balance. Your veterinarian should provide perspective and be objective and well-informed about cancer, it's treatment, and how it is likely to affect your pet. On the other hand, you know your pet the best?the veterinary staff sees your pet for perhaps a few hours a week in a hospital setting, while you and your family are with your pet at home on a daily basis.
Cancer treatment usually involves side effects, which can affect a pet's quality of life. The degree of side effects that are tolerable depend on the goal and expected outcome of treatment. If our hope is for a cure or control of cancer (which in veterinary medicine usually means one year or longer), then we may be willing to tolerate treatment side effects with a higher risk, severity, and duration. Several days or weeks of decreased quality seems reasonable in exchange for many months of good quality of life. However, if we believe a cancer is incurable or impossible to control, then our goals become those of palliation, which is an attempt to maintain or improve quality of life without attempting to prolong it. We are unwilling to accept anything but minimal treatment side effects because the treatment should not be worse than the disease. Palliative care focuses on supportive measures such as controlling pain and infection, and providing adequate nutrition. Every owner and veterinarian will have their own opinion as to what constitutes acceptable and unacceptable risks and side effects. It is important to thoroughly discuss these concerns with your veterinarian so that together you can work towards a common goal.
Because we cannot ask our pets how they feel, we have to rely on their behavior and from this infer quality of life. Measurements of quality of life have been developed by veterinary oncologists. For example, the Animal Medical Center in New York City developed a "Performance Scale" that allows both the pet's family and the veterinarian to assess overall quality of life. It considers 5 factors that affect an animal's ability to carry on its normal activities.
Not only is this assessment a good indicator of how your pet feels overall, it also provides useful medical information. In general, animals that score high (i.e., have close to normal behaviors) tend to tolerate treatments well and do better overall than animals who score lower on the scale.
Quality of life means different things to different people. For some people it is their pet's chasing a ball or greeting them at the door. For others, it is simply knowing that pets are eating and sleeping through relaxing, painless days. One of the difficulties in evaluating your pet's quality of life is that it can decline gradually. For someone living with a pet there may be no obvious daily changes, while to someone who only sees your pet every few weeks or months there could be dramatic change. Because of this, we encourage owners to establish and document their own personal "minimum standards" of quality of life for their pet at the start of cancer treatment. For example, it might be a pet's lack of interest in eating or going on walks. It might be a pet's struggling to breathe or inability to "get comfortable". Often, it is a pet's inability to respond to his owners or his struggle to muster even a small gesture of affection. Thinking about these issues and discussing them with your family and veterinarian early in the course of therapy can help with difficult decisions later on, such as discontinuing treatment or electing euthanasia.
There often comes a point in the treatment of our veterinary cancer patients when we have exhausted all reasonable treatment options, and there is a low probability for quality of life in the future. We must remember that just because a treatment is technically possible does not mean that it is the best thing for our patient. We are then faced with euthanasia as the last treatment option. Just as we have intervened in the pets life by providing aggressive medical care in an effort to improve and prolong quality of life, we intervene when these methods are no longer effective so that we do not prolong needless suffering. It is the last act of kindness we can offer.