Steve Connor: This could revolutionise our view of the disease

One in three people in the developed world will develop cancer at some time in their lives and one in five will die of their illness. As all tumours are the result of abnormalities in our DNA, it follows that cancer is the most common genetic disease.

Breast cancer is a particularly poignant form of the illness. It is the most common cancer in the UK and each year nearly 48,000 women are newly diagnosed, a substantial minority of whom are in their 30s and 40s.

Like many tumours, the survival rates for breast cancer have steadily improved over the past 25 years, helped by new classes of drugs targeted at women carrying specific cellular "markers", such as the HER2 receptor protein.

In the 1970s, about 50 per cent of those who were diagnosed with the disease survived beyond five years; the figure is now about 80 per cent, thanks largely to better and earlier diagnoses.

Although breast cancer is the most common cancer in women, it is not the most lethal. Lung cancer still kills more women because it has proved harder to treat. The latest study into the genetic basis of breast cancer highlights just how simplistic our view of the disease has been in the past.

For half a century or more, medical students were taught that cancer is not one disease but many. Now scientists are saying that breast cancer is an umbrella term for at least 10 different subtypes of the disease.

It is more than likely that our view of other cancers will be changed in a similar way as a result of the scientific and technological revolution taking place within cancer research centres.

It is now more than 30 years since scientists identified the first "tumour suppressor" gene, known as p53, and 20 years since they discovered BRCA1, another gene that normally suppresses cell division and cancer.

Mutations in these genes significantly increase the risk of inherited forms of cancer. Their discoveries gave the first important insights into the genetic basis of tumour suppression and development. Scientists have since been able to focus on the far more common cases of non-inherited cancer that appear to develop sporadically within a person's body, sometimes as a result of toxins. The new genetics, based on the unravelling of the human genome, is showing scientists how to identify the sporadic or "somatic" mutations in our DNA. It marks a true revolution in the understanding and treatment of a set of diseases that is likely to affect many of us, or someone close to us, at some point in our lives.