Cancer is one of the first areas being affected by pharmacogenetics.

Cancer is a genetic disease. Because of inherited or new mutations, cells lose the ability to control growth and replication, and multiply out of control.

Mutations in many different genes can cause cancer, and a particular type of cancer - breast cancer, for instance - may be caused by mutations in a number of genes. But drugs can be targeted at specific genetic flaws within cancer cells.

A classic example of this is the a drug used to treat breast cancer, called Herceptin (also known as trastuzumab). This drug is targeted at a protein known as HER2. Around 20-30% of cancers have high levels of HER2 on their surface of their cells. A test can identify women who have cancers likely to respond to the drug. (Strictly speaking, this is not a pharmacogenetic test as it assesses HER2 protein levels rather than looking the DNA sequence of the HER2 gene, but the principle is the same.)

Another good example of targeted cancer treatment is Glivec (imatinib). This therapy is specifically-used to treat a type of leukaemia caused by a characteristic chromosomal rearrangement. This rearrangement creates a mutant growth-promoting protein in white blood cells that causes them to become cancerous. The drug recognises this mutant protein, so will only work on leukaemias in which it is present.

These cases illustrate how drugs are increasingly being developed on the basis of known disease mechanisms. This is called rational drug design. It is an important way in which pharmacogenetic research is impacting on drug development. Identifying genes and proteins involved in disease processes reveals targets for drug development.

Traditionally, cancer therapy has targeted dividing cells in the body - but cancer cells are not the only dividing cells in the body, so cancer treatments tend to have many side-effects. Rational therapies are more specific, but each is likely to be suitable for only a few tumour types.

Cancer is a disease which is being studied extensively using pharmacogenomics. This is because the disease has a strong genetic component and not many therapies are available. An untreatable cancer is generally fatal - so new treatments are urgently needed.