Billions of cells in our body, growing, dividing, carrying out their manifold functions, growing, dividing, degenerating, dying. These are the microscopic workhorses of the body, the ordinary foot soldiers that carry on and win the endless battles that assure survival of the organism as a whole. Like soldiers they receive commands – through hormones and other chemical messengers, through contact with their neighbours or nervous system signals – and these commands they obey. There are rules, instructions, hierarchy, routine. And all is well, and all functions as it should.
Until a single cell rebels. The soldier who would be general suddenly stops being controlled and assumes command, becoming an autonomous renegade. It is wildly different from its neighbouring cells and begins to divide more rapidly than them, making copies of itself at a prodigious rate. The mass of rapidly growing cells in this clone expand and impinge upon the normal cells adjacent to them. The normal cells shrivel up and die. All the while, the mass of renegade cells keeps on growing larger. They obey no more signals, they are not under the body’s control any more.
And as time passes, things may get worse. The rapidly growing cells infiltrate the space between the normal cells and grow between them. They invade the surrounding normal tissues and mingle imperceptibly with them. All the worse is that they still masquerade as our own cells, our body still sees them as belonging to it, misled by their lineage. Usually by the time the body recognises that they are renegades and mounts a defence against them it is too late. The tumour is too large and unable to be controlled.
These cancerous cells will rarely cause pain or other early warning symptoms. As they grow further they may invade body vessels and being more likely than normal cells to become detached from their neighbours, they will break off in small clumps and move through the body vessels to distant parts of the body. Once there, each of these groups of cells will grow and become a new colony, each colony destroying more normal tissue, undermining more and more of the body’s vital functions. If there is no intervention, malignant renegade cells like these will kill the very body that hosts. A Pyrrhic victory for a renegade soldier turned to mad general…
Such is the life and death natural history of a cancer. We know a lot about what makes a cell cancerous. Ultimately every cancer is due to a mutation. A mutation is a change in the genetic material of a cell – the DNA – that can be inherited by daughter cells as the mutant cell divides. Mutations in the DNA can be harmless, causing little or no change in function, to fatal mutations that kill the cell. Somewhere in between these two extremes is the disrupted function that we know as cancer. Uncontrolled, autonomous, excessive growth that continues and allows the abnormal cell to make more and more of itself, the cancerous mass serving no useful purpose in the body.
As to what causes the mutation in the DNA, in some cases we know for sure. For example, radiation such as ultraviolet light, X-rays and gamma rays can directly damage DNA and cause mutations. That is why we should use sunscreen when we are out in the sun: To protect our skin cells from the mutating effects of sunlight’s ultraviolet radiation. A small number of viruses under special circumstances can cause cancers by mutating the cells they infect. For example, the genital warts virus in women causes cancer of the cervix – hence the vaccine that is now being used to prevent it. Our diet can cause mutations in the cells lining the gut. We know that certain foods that we eat habitually will over a long time cause cancers of the gut. For example, pickled, smoked and other preserved foods are associated with cancers of the stomach. A diet high in red meat and saturated fats while low in fibre, fresh fruits and vegetables will cause cancer of the large bowel.
We know of a huge number of chemicals that cause cancers. Perhaps the best documented example is that cocktail of about 200 chemicals that smokers inhale with each puff of smoke from a cigarette. These chemicals are irritants that cause damage and inflammation, they are carcinogens that directly damage the DNA of cells and many of them are promoter chemicals that help cancer cells grow faster once they have formed. Smoking is the foremost cause of lung cancer. Before smoking became widespread in the early 20th century, this cancer was a rarity. Most cases of lung cancer that we see occur in heavy smokers.
Hormones and other internal factors can be traced to cancer causation in genetically predisposed people. The prime example is breast cancer, which is influenced by secretion of female hormones, whether or not a woman has had a child (and at what age – the younger a woman becomes a mother the more protected she is from developing this cancer) and whether there is breast cancer history in the woman’s sister, mother or grandmother.
However, despite the examples of known cancer causes given above and quite a few more that we are aware of, there are many cancers that seemingly arise out of the blue with no known predisposing factors that we can demonstrate. Some of these occur in genetically predisposed people. Some families are more prone to develop cancers as they carry assortments of faulty genes that can spontaneously mutate, or be more likely to mutate in circumstances that genes in normal people will not. It is indisputable that cancer development is linked to genetic factors some of which we understand, some of which we still are researching. Some cancers arise out of the blue spontaneously in people who logically should not get them (remember my friend from yesterday’s post?). These random, sporadic cancers are the most difficult to understand, but fortunately they are rare.
Many cancers can be cured effectively nowadays. Cutting the tumour out is the most obvious treatment and surgery remains the cornerstone of cancer treatment for the majority of cancers. Drugs can be used to selectively kill the cancer cells and this is the principle of chemotherapy. This is the only option with some widespread cancers like leukaemia. Yet another treatment is radiotherapy where high energy radiation is used to kill the cancer cells, which are more susceptible to damage than normal cells are. Many brain cancers are often treated in this way, given their vital position and high risk of damage to normal tissue through surgery. New treatments for cancer include combinations of the above, but also there are newly developed treatments with immune system modulators and monoclonal antibodies against cancer cells.
Prevention is still the best option for reducing our risk of dying of cancer. We know that preventing our exposure to many of the substances that are known to cause cancer will reduce our risk of developing the disease. Taking care of our diet, exercising and keeping fit, limiting our exposure to ultraviolet light, protecting ourselves against viral infections that are associated with cancer through vaccination (in particular Hepatitis B and Genital Warts), having appropriate tests to catch cancer early and have it cured, all can all help us live a cancer-free life.
cancer |ˈkansər| noun
The disease caused by an uncontrolled division of abnormal cells in a part of the body: He's got cancer | Smoking is the major cause of lung cancer.
• A malignant growth or tumour resulting from such a division of cells: Most skin cancers are curable by surgery.
• A practice or phenomenon perceived to be evil or destructive and hard to contain or eradicate: Racism is a cancer sweeping across Europe.
DERIVATIVES
cancerous |ˈkansərəs|adjective
ORIGIN Old English, from Latin, ‘crab or creeping ulcer,’ translating Greek karkinos, said to have been applied to such tumors because the swollen veins around them resembled the limbs of a crab. Canker was the usual form until the 17th century.
