Doctors use all kinds of terms for cancer - malignancy, carcinoma, lymphoma, tumor, and so on. Most people just see cancer as a word for a bad disease, which can act like a parasite and destroy the body. There is no single cause of cancer, or even of each individual form of the disease.

Two unique characteristics of cancer cells create the deadly nature of this disease. First, cancer cells may spread to adjacent areas and invade normal tissues and organs, depriving them of nutrition and competing for space. Second, these cells may travel to a distant part of the body where they begin the development of another tumor, called a metastasis. The most common sites of metastasis spread are the bones, lungs, liver, brain, and central nervous system. We all have cancer cells in our bodies. They develop naturally all the time. Usually, the body's immune system disposes of these cells. When this process of self-defense stops for some reason, a tumor begins to develop.

From the point of view of medical professionals, compared to some other life-threatening diseases, cancer more often can be managed. The time course is one more understood and most people are still able to take care of themselves and stay mentally alert until close to the end. These characteristics also make cancer the most terrible of diseases for those who suffer it. The sick person has the time and lucidity to feel all the tragedy, pain and inevitability of the situation they are in. Cancer has two devastating effects, which often appear together. It induces long term, debilitating exhaustion and acute, agonizing pain.

Early in the course of dealing with cancer, treatments aim mostly at a cure or at least a substantial lengthening of life. With these goals, it is certainly worth going through a lot of discomfort.

However, when cancer recurs or spreads despite treatment, then the cancer is likely to cause death eventually. The benefits of further treatment aimed at modifying the cancer must always be weighed against the burdens those treatments will cause. Usually, the time comes when all of the available treatments to change the course of the cancer offer nothing worthwhile. Throughout this, treatments are always appropriate when they enhance comfort, improve the patient’s functioning, and support families.

Even when there is nothing more to do about the cancer growth, there's lots to do to maintain comfort and give the terminally ill the chance to do the things that are meaningful to them and to their loved ones. When treatments won’t really change the time course of the cancer, patients still need comfort care, or what doctors call palliation, the relief of symptoms that affect the quality of life. In fact, patients should aim to live well throughout the course of their illness, pursuing those personal goals that they can achieve while remaining comfortable all the time.