There are only two good things to be said about cancer: some can be cured, and some are not painful. Cancer is completely different from the painful conditions we have just described in which the cause of the pain is associated with tissue that has been smashed and is in the very abnormal state that causes inflammation. Cancer cells are almost exactly like normal cells except that they are multiplying. For this reason, the body does not recognize them as foreigners and therefore sets up none of the normal defensive inflammatory responses to react to them. This means that cancer in its early stages is painless except on very rare occasions. This is a terrible disadvantage because the lack of pain signals at this initial phase means that diagnosis is delayed.
The body has an elaborate and precise mechanism for recognizing foreign objects, including cells. This defence mechanism explains why transplants, or grafting of tissue from other people, never works unless the immune system is suppressed. Cancer cells grow by stealth, accepted by the neighbours as normal. They may grow as a solid lump or may invade between neighbouring cells and infiltrate over long distances. Cancer cells may float free in the bloodstream or in the ducts of the lymphatic system and lodge elsewhere to establish colonies called metastases. During this stage, the victims are unaware that they are host to a silent invader.
In a recent case, a high-ranking air-force officer made a faulty landing on a carrier deck. As the plane careered out of control, he activated his ejector seat and was safely rescued. Because firing the ejector-seat rockets puts very heavy g-forces on the body, it is routine to carry out an X-ray examination of the entire body to search for small bone fractures that may have occurred. In this routine scan, it was discovered that this apparently healthy man, who had recently passed a rigorous medical check, had a sizeable brain tumour which was producing no signs and, certainly, no pain.
If cancer is silent in its early stages, why does it have such a reputation as a painful disorder? The answer is that the swelling lump eventually causes pressure. As brain tumours grow they block the drainage of the fluid in which the brain floats, pressure rises in the head, and headaches result. Tumours in the gut grow to such a size that they block the normal passage and painful cramps result. Tumours may block blood vessels, producing pain in tissue starved of oxygen. Lung cancer becomes painful only when it blocks small air passages and local inflammation attempts to remove the sick area of lung. Bone tumours are painful because they press on the sensitive covering of bone. They may also produce pain by weakening the bone so that it fractures.
These secondary pressure effects explain at least 80 per cent of cancer pains. Surgery may produce a dramatic beneficial effect on these pains by relieving the pressure block even if it does not cure the cancer. Similarly, X-rays and chemotherapy may have excellent palliative effects by shrinking the lumps. Only a few quite rare cancers, such as those produced by asbestos, emit pain-producing substances, making the cancers painful by themselves before they reach the pressure-pain stage.
One type of cancer pain comes from nerve damage which itself is caused by pressure when the cancer infiltrates major nerves. We will discuss why this is so painful in the next section on amputation, which causes the major problems from nerve damage. Unfortunately, pain may be a side effect of treatment. This is a crucial area of the relationship between doctors and patients in which a full explanation must be given about the balance between the chance that therapy will cure or ameliorate the cancer and the chance that therapy will produce devastating side effects. Radical surgery followed by radiation treatment to remove an entire breast with its cancer and all the lymph tissue in the armpit, which may contain spreading cancer, gives the patients a chance that they may survive five or ten years or longer. However, while the patient decides to take this gamble, they must understand that there is a chance that the treatment may also leave them with disabling pain. We carry out this grim balancing of risk versus benefit throughout our lives, but there is no time when an honest, open assessment is needed more than when a patient considers treatment for his or her cancer.
Cancer pain is worse than useless. It provides absolutely no protective signal because the disease is far advanced before it starts. Once started, it announces the obvious and, if it goes untreated, it simply adds to the miseries of impending death. Worse, untreated pain accelerates death. Fortunately, the great majority of these pains can now be treated to bring real comfort to the dying patient.
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Pain Relief
