The genetics of 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!

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 the start of the malignant process. The clue to why one person gets cancer and another does not, despite the same lifestyle probably lies in their genetic makeup – the cards they were dealt. Some people may have been born with a rather loose arrangement between their good and bad genes which could be separated by low carcinogen exposure in an apparently healthy lifestyle. Alternatively they could have an inherited defect in their suppressor genes. Examples of these include

• The BCRA-1 or BCRA-2 gene mutation which increases the risk of breast & ovary cancer 

• The hereditary polyposis coli gene for bowel cancer.

• Von Hippel Lindau syndrome for kidney cancer

• Li'fraumany syndrome for sarcomas and other cancers

• Other very rare syndromes include Browns syndrome, Morlyn's sundrome

On the other hand some people are fortunate to be born with their cancer genes locked in tightly by very stable suppresser genes resulting in a very robust DNA profile the has been no names given to these - people with these DNA profiles are simply called lucky! It will take an awful lot of chemicals in these individuals 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, eats rubbish all his life and didn't get cancer". Most people, however 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.

On top of these inherent genetic risks, environmental risks factors rearrange the DNA triggering the start of the cancer process. These factors include:-

• Dietary cancer causing chemicals (carcinogens) such as polycyclic aromatic hydrocarbons and aromatic amines, found in superheated processed or fried foods.
• Viruses can also infect cells and damage the DNA – the most well known of these being the Human Papilloma (wart) virus and cervical cancer or a virus found in Africa called the Ebstein-barr virus causing a cancer of the lymph nodes (Burkitt’s Lymphoma).
• Radiation and sunlight can also directly damage DNA. In fact, a few hours in the sun can result in hundreds of potential skin cancers.