A blood test that detects breast cancer more than a year before any symptoms appear could dramatically improve survival rates.
The test looks for raised levels of a certain protein that is already known to increase once cancer has developed. But in a new study, researchers found levels of the protein, called epidermal growth factor receptor, were already high up to 17 months before women were diagnosed with breast cancer.
The test, announced at the recent annual meeting of the American Association for Cancer Research in Washington DC, could herald a breakthrough in the search for a so-called 'biomarker' that indicates the presence of cancer before the patient or doctors suspect anything is wrong.
Numerous research teams around the world are searching for such biomarkers for a range of different cancers. This is because the earlier patients begin taking anti-cancer treatment, such as tumour-shrinking drugs, the better their chances of making a full recovery.
The search for a breast cancer biomarker that can detect the presence of minute amounts of malignant cells is seen as a major priority.
Screening in the UK relies on mammography, where an X-ray image of breast tissue is taken and then analysed visually by trained technicians.
Between the ages of 50 and 70, all women are called for routine screening every three years on the NHS.
Those with a strong family history of the disease at a young age may be screened from their 20s or 30s. But there have been concerns over the accuracy of some mammography scans.
In 2008, for example, thousands of women in the Manchester area were affected when health chiefs were alerted to errors by one technician.
They then ordered a review of scans dating back to April 2003. The other problem is that X-rays do not easily penetrate dense breast tissue found in younger women, reducing the chances of finding small tumours.
Women also complain that the actual procedure can be extremely uncomfortable, as the breast has to be compressed between plates for an image to be taken.
The latest development came from a study of more than 400 breast cancer victims by scientists at the Fred Hutchinson Cancer Research Centre in Seattle.
The volunteers were all taking part in a major, long-running U.S. study, called the Women's Health Initiative, a 15-year investigation that began in 1991 and involved more than 100,000 volunteers.
Every volunteer donated blood samples to the study for routine testing. When researchers identified women who later developed breast cancer, they analysed the blood samples they had given up to 17 months before their diagnosis.
These were then compared with another group of cancer-free women from the same study.
The results showed those with the highest levels of epidermal growth factor receptor were nearly three times more likely to be diagnosed with cancer at a later date.
It's not clear yet whether the test can predict cancer even further into the future, as 17 months was the nominated cut-off point.
Epidermal growth factor receptor is a protein on the surface of all cells. But in excess quantities, it can trigger uncontrolled growth of cancerous tissue.
Dr Christopher Li, who led the research, said it was too early for the biomarker test to be used on its own as a cancer diagnosis. But it could form part of the screening process if further trials confirm the early findings.
'No prior studies have validated a single breast cancer early detection biomarker to the degree that we have here,' he said.
Dr Claire Knight, Cancer Research UK's health information officer, said: 'This work is still at an early stage, and it's not yet possible to tell if this research could be developed into an effective test.
'However, biomarkers are an exciting area of research because they could flag the early stages of certain cancers, making diagnosis much quicker and easier in future.'
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