Breast cancer is found in one in three women between regular screenings, according to a new study.
In the first study of its kind, researchers at the Institute of Cancer Research analysed data from over 7.3 million women who were routinely screened between april 1997 and march 2003 in England, Wales and Northern Ireland.
They found that 2.91 per 1,000 women who had been given the all-clear at a screening were found to have been diagnosed with breast cancer before their next screening.
The cancers are mostly picked up because the women start developing symptoms, such as a lump in the breast.
These “interval cancers” include tumours that grow between screening appointments, as well as those that are missed or are undetectable during mammograms.
Experts behind the research said reducing the length of time between mammograms could lead to more cancers being detected but may not have an impact on death rates.
Women in the UK aged 50 and over are invited for NHS breast screening every three years.
Around 1.5 million women are screened annually and the programme is in the process of being extended to all women aged 47 to 73.
Senior author Dr Sue Moss said: “The rate at which women developed breast cancer between screenings was higher than expected, and is likely to reflect the fact that breast cancer rates are rising in general.
“Reducing the length of time between screenings would result in a lower proportion of interval cancers, but not necessarily a significant reduction in mortality.”
- Bennett RL, Sellars SJ and Moss SM. Interval cancers in the NHS breast cancer screening programme in England, Wales and Northern Ireland. British Journal of Cancer 2011; 104, 571-577.
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