The most crucial aspect of any cell is arguably its DNA. DNA can be thought of as a biological molecule that acts a blueprint. Just like with a building, the blueprint explains the shape, size and how different parts will interact with each other. DNA tells each cell whether it will be a hair, tooth, skin, heart, brain or any other cell. It also controls how long each cell will survive and tells it when it should start and stop dividing (for the purpose of growth and or repair). Because DNA is so important, our cells have various protective mechanisms to ensure that instructions encoded within DNA are preserved.
Cancers occur when either our DNA repair mechanisms are damaged or damage occurs directly within the DNA, and the cell is unable to repair it. In human cells we have two copies of DNA, one from each parent. Having two copies essentially provides us with a kind of backup. If a gene (particular areas of DNA that code for specific instruction) gets damaged on one copy, we can rely on the healthy gene on the other copy. The problem occurs when both copies of a gene become damaged. If the damaged gene carries instructions that control the growth of the cell, then this could result in a cell that begins to divide in an uncontrollable manner. It is important to note that in most cancers it is likely damage occurs to multiple sets of genes, also other factors, for example how surrounding cells interact with the abnormal cell, will influence whether a cancer will occur.
Carcinogens impair our DNA repair machinery. In most cases, the greater the exposure (i.e. the longer you smoke, the heavier you drink, the more time you spend in the sun without protection), the more damage your doing to your DNA's repair mechanisms, and the more you are increasing your risks of developing certain cancers.
Certain viruses have been implicated in causing particular cancers. The most well known example of this is the Human Papilloma Virus (HPV). Particular strains of this virus are known to be cancer inducing. These strains are thought to cause cancer by incorporating it's DNA into ours. This causes damage to our own DNA. HPV is the main cause of cervical cancer. HPV is normally sexually transmitted and so women who have unprotected sex with multiple partners will increase their risk of exposure to this cancer causing virus.
As well as external factors, our own bodies produce molecules that can damage DNA. These are known as free radicals. They are byproducts of normal chemical reactions in cells. Free radicals are energetic molecules, which can attack and damage DNA.
1. Cancer Research UK. Summary of cancer incidence and mortality in the UK. Available at http://info.cancerresearchuk.org/prod_consump/groups/cr_common/@nre/@sta/documents/generalcontent/018070.pdf (Accessed: 24 January 2010).
2. William, D.F. Inherited Susceptibility to Common Cancers. The New England Journal of Medicine, 359(20), 2008, pp. 2143-2153
