What causes cells to become cancer?

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Within each cell, in the human body, lies a structure called a nucleus, containing strips of material called DNA. To be precise 46 strips each containing millions of packages of information called genes. These genes are the codes and templates for all the functions of the entire human body. They have evolved over the centuries through countless generations to produce the human form we know today. 

Over this time our genes have picked up considerable amount of debris. Some of this debris includes strips of genes which actual cause cancer but are kept from mischief by other genes which lie next to them on the same strip of DNA. These good genes, called tumour suppresser genes, were themselves once randomly picked up through the evolutionary pathway but now serve the essential function of guarding the body from the bad cancer genes - we would get cancer without them. Essentially we were born with the tendency to get cancer - its part of us!

A good analogy to explain this in more detail is with the machine you are currently using - a personal computers and the problem of computer viruses. -- Imagine there were no virus checkers and we started with 100 computers. If we then exposed each computer to numerous viruses at random of a period of years, each time the computer is turned on would be equivalent a generation in the human race. Many computers would be so infected they would cease to function very quickly. In other infected computers, it is possible that a subsequent virus could actually attack a previously virus deactivating it before it harms the host computer. The computers that eventually remain functioning would have numerous viruses in its system interacting and de-activating each other but not causing significant harm. This is precisely what has happened to the human race but there are literally hundreds of thousands of viruses or jailer genes guarding a similar number of cancer genes. A very precarious situation indeed - any damage to the DNA even slightly could move a bad gene away from its jailers and cancer develops.

 With thousands of potential cancers already programmed in our DNA it does not come as a surprise that 1 in 3 of us will get cancer at one stage in our lives. Perhaps instead of asking why me when we develop cancer we should be asking why not me when we don't?

With cancer already coded in our DNA guarded by other anti-cancer genes any re-arrangement of the DNA can lead to serious consequences. What then can damage DNA? The simple answer is life. Virtually any chemical in the right concentration and environment can be harmful. Some are, of course, more dangerous than others, cigarette smoke for example. Radiation and sunlight are also powerful DNA damages. In fact, a few hours in the sun can result in hundreds of potential skin cancers. Of course only a few of us will eventually develop skin cancer which indicates that the body does have other defences against cancer. The most well known of these is a gene nicknamed the cellular policeman. If a cell is partially damaged this policeman slows down the cell cycle and allows DNA repair to take place - if repair is not possible it does not allow the cell to divide with rearranged DNA which could eventually cause cancer. Instead it programs the cell to commit suicide - this is called programmed cell death or in the trade apoptosis.

Some people are born with a defect in this policeman gene (known as p53). As you can imagine they usually develop multiple cancers at a very early age in life. This condition is called li'fraumany syndrome and is an extreme example of why some people get cancer despite living a healthy life. Others fortunate to be born with the cancer genes locked in tightly by very stable suppresser genes have a very robust DNA profile. It will take an awful lot of chemicals to damage the genes enough to cause cancer. These extreme cases are often quoted as excuses for hardened smokers. "He smoked 20 cigarettes a day, eat rubbish all his life and didn't get cancer". Most people are somewhere in between these two extremes so although we have an underlying risk of developing cancer which is outside our control what we do to our bodies still has a great influences on our destiny. Eating fresh fruit and vegetables, regular exercise, avoiding excessive meat intake, dietary chemical, smoking, industrial chemicals and radiation are obvious examples.

The medical profession is trying strategies which pick up cancers early by, for example, screening people at vulnerable periods of their life for cancers such as breast and cervix. This is a time consuming and costly service that still misses a great number of people. Scientist are trying to help by identifying genes in our genetic makeup which make us more susceptible to a particular type of cancer - some have already been found. For example, if a patient has a defect in a gene called BCR-1 or BCR-2 the risk of breast cancer increases ten fold. These ladies could be screened at an early age more intensively ensuring early detection when it arises. Eventually it may even be possible to infect these individuals with the corrected genes grown in the laboratory which then prevent the cancer developing in the first place! This idea is a long way off and in the mean time we have to rely on early detection and the conventional treatments of surgery, radiotherapy, hormones and chemotherapy.