(The Lancet) -- Annual screening, using magnetic resonance imaging (MRI) and X-ray mammography, is the best way to detect breast cancer in women that have a high genetic risk of the disease, according to a study published online today by The Lancet.

Women who have mutations in genes called BRCA1 and BRCA2 have a high risk of developing breast cancer, often at an early age.

Regular mammograms are offered to high-risk women to allow for the early identification and treatment of tumours. However, because these womenare of a young age, they often have denser breasts, which affect the ability of mammography to detect disease.

Martin Leach (The Institute of Cancer Research, London, UK) and colleagues looked at whether MRI would be more effective than mammography in detecting breast tumours in high-risk women.

Between August 1997 and May 2004, the investigators recruited around 650 women at high risk of breast cancer, from 22 radiology and genetic centres throughout the UK. The women, aged 35 to 49 years, were offered annual MRI and X-ray mammography for between two and seven years.

They found that MRI was nearly twice as sensitive as X-ray mammography in detecting breast cancer in women that have a high genetic risk of the disease. X-ray mammography identified 40% of the tumours in the women, while MRI detected 77%. However, when mammography and MRI were combined, 94% of tumours were picked up in the women.

The researchers also found that MRI screening was particularly effective for women known to carry the BRCA1 gene mutation, detecting 92% of tumours in women carrying this gene whereas X-ray mammography only detected 23%.

Professor Leach states: "Our results, taken with the two other major prospective studies, suggest that MRI screening is more effective than mammography in this high risk group, and combining the methods is very effective. Our study also showed that MRI is of most benefit in carriers of BRCA1 mutations."

In an accompanying Comment Ellen Warner (Toronto-Sunnybrook Regional Cancer Centre, Ontario, Canada) points out: "Although there is now unequivocal evidence that surveillance MRI is significantly more sensitive than mammography for women at high hereditary risk and detects cancers at an earlier stage, it is not yet known whether it will lower mortality in this population."