A panel of experts led by University College London professor Sir Michael Marmot concluded that screening prevents about 1,300 deaths per year in Britain but can also lead to about 4,000 women having treatment for a condition that would never have troubled them.
This means that for every death that is prevented, three women are over-diagnosed.
The review panel called for improved information, in health leaflets for instance, to give women a clearer picture of both the benefits and potential harms before they go for a mammogram.
Breast cancer is the most common form of cancer among women in Britain, affecting one in eight at some point in their lives. The country’s screening program invites women aged 50 to 70 for a mammogram every three years and this is being expanded to ages 47 and 73.
Earlier diagnosis and better treatments have improved the survival rate to 77 percent in 2007 from 41 percent in 1971, according to CRUK.
The conclusions of the review are based on analysis of 11 trials that all took place more than 20 years ago, which assessed whether screening resulted in fewer deaths due to the disease, compared to when no screening takes place.
The panel acknowledged the studies had limitations, not least because of their age, but decided the evidence was strong enough to conclude that women invited for screening have a relative risk of dying from breast cancer that is 20 percent less than those who are not invited.
Harpal Kumar said research is under way that could lead to more sophisticated tests that distinguish aggressive cancers from those that are not.
This, coupled with a better understanding of genetic predisposition and lifestyle factors that play a role in breast cancer, could mean more finely targeted screening and less over-diagnosis.
“Until this is possible, we’d recommend women who have had something unusual picked up through screening to seek full advice and discuss all possible options with their breast cancer specialist team,” he said.