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Can understanding genes help?

Several types of genes can change in a cancer cell: genes that control cell growth, cell death and cell movement, and genes that repair DNA damage. Since 1975 scientists have tracked down hundreds of genes involved in cancer. Changes in just a few of them can turn a healthy working cell into a cancerous one. Knowing their identity will allow scientists to devise new ways to fight cancer.

Changes in the ras protein - a growth 'accelerator' - are found in many tumours.

How could therapies target growth control genes?

A cell continuously receives messages, both from its own genes and from other cells. Some messages tell it to grow, and some tell it to stop and rest - like the accelerator and brake pedals in a car. Mutations to some genes cause uncontrolled growth by jamming down the accelerator. These genes are known as oncogenes. Mutations in other genes, cause the brakes to fail, with the same effect. These genes are called tumour suppressor genes. Some new cancer therapies are targeting these cell growth control genes.

'Accelerators' - or oncogenes - tell a cell to grow or divide, while 'brakes' - or tumour suppressor genes - tell a cell to stop.

Would slowing down growth help?

Some new therapies for cancer aim to target and kill cells that contain abnormal genes. Several new medicines aim to block the genes responsible for jamming down the accelerators. Different genes are damaged in different cancers, so these new therapies could be tailored to treat individual tumours.

Computer analysis of 22500 different human genes, which have been analysed for any changes that occur in their expression patterns between normal and cancerous cells.

What is the role of p53?

One of the most frequently altered genes in cancer is for a protein - p53 - which monitors DNA damage. When DNA in a cell is too damaged, p53 normally sends a signal that tells the cell to commit suicide. When p53 is lost in tumours, this vital protection is absent. Scientists are experimenting with gene therapy, which one day might be used to replace the normal p53 gene in tumours. Another approach uses a virus - called ONYX-015 - that only attacks and kills those cancer cells without working p53.

ONYX-015 (arrowed) infection in cancer cells.