A British panel has determined that while breast cancer screening for women over age 50 saves lives, it also leads to overdiagnosis.
According to an article published last week in the Lancet, the panel, commissioned by Cancer Research UK and Britain's department of health, analyzed data from 11 trials in Canada, the U.S., the U.K. and Sweden, and determined that women who undergo screenings have a relative risk of dying from cancer that is 20 percent lower than those who aren't screened.
While acknowledging these trials have limitations--most occurred over 20 years ago--the panel concluded that the 20 percent figure is still a reliable one. The panel also determined that estimates from trials and observational studies support the occurrence of overdiagnosis--the diagnosis of slow growing breast cancers that would never cause harm--from screening, although the magnitude of overdiagnosis is unclear.
The panel estimated that for every 10,000 women in the U.K. aged 50 years who will undergo screening over the next 20 years, 43 deaths from breast cancer will be prevented and 129 cases will be overdiagnosed. It went on to calculate that of the 307,000 women between the age of 50 and 52 who are invited to begin screening every year, slightly more than 1 percent will have an overdiagnosed cancer in the next 20 years.
"It was extremely important to look at all the available evidence surrounding both the achievements and shortcomings of the U.K. Breast Screening Programs in the wake of increasing debate over their effectiveness," Sir Michael Marmot, professor of epidemiology and public health and director of the Institute of Health Equity at University College London and panel chairman, said in a statement. "The Panel concluded that the screening programs have contributed to reducing deaths from breast cancer in women. But they have also resulted in some overdiagnosis among women who go for screening. It is now vital to give women information that is clear and accessible before they go for a mammogram so they can understand both the potential harms and benefits of the process."
Harpal Kumar, chief executive of Cancer Research UK, said in an official statement on the review from Cancer Research UK, that the independent review shows screening saves lives. "Yet, as the review shows, some cancers will be diagnosed and treated that would never have caused any harm. Clearly, everyone wants to minimize this. But, because we can't yet tell which cancers are harmful and which are not, we cannot predict what will happen in an individual woman's case."