Breast Cancer Screening Exposed As Near-Useless: 2,970 Women Must Be Screened to Save One

A new study has cast fresh doubt on the widespread assumption that regular mammograms save lives, showing that 2,970 women must be screened for breast cancer in order to prevent even one death.

"For a woman in the screening subset of mammography-detectable cancers, there is a less than 5 percent chance that a mammogram will save her life," wrote the researchers from the University of Nebraska and the John H. Stroger Jr. Hospital of Cook County, Ill. "By comparing mammography's life-saving absolute benefit with its expected harms, a well-informed woman along with her physician can make a reasonable decision to screen or not to screen for breast cancer."

Breast cancer is the most common cause of cancer death among women and the fifth most common cause of overall cancer death worldwide. An estimated 1.2 million new cases are diagnosed around the world each year, leading to 500,000 deaths.

A mammogram uses X-ray radiation to take an image of the breast that can then be evaluated for irregularities such as tumors. U.S. federal guidelines recommend that all women aged 40 and above receive a mammogram once every one to two years.

In the new study, published in the journal BioMed Central Medical Informatics and Decision Making, researchers examined breast cancer screening and mortality data from a variety of different sources. They found that the benefit of mammograms in saving lives increased gradually with age, corresponding to the increase in the overall risk of breast cancer death (independent of screening).

A woman's absolute risk of developing breast cancer between the ages of 55 and 70 is approximately 6 percent, with a 1 percent chance of breast cancer causing her death. The researchers concluded that starting at age 50, 1.8 lives would be saved for every 1,000 women who was screened consistently for 15 years.

"In other words," the researchers wrote, "2,970 women must be screened once to save one life."

This means that undergoing regular cancer screening at age 40 only decreases a woman's risk of dying from cancer by 0.1 percent. Another way of putting the same data is that out of every 23 cancers detected, one life will be saved.

Researcher and radiologist John Keen emphasized that he does not believe mammograms are useless, and that he performs the procedures himself. He does not believe, however, that women and doctors have a realistic understanding of what benefits regular breast cancer screening can actually provide.

"The people who are promoting screening are not explaining it," he said. "They are pushing the wrong statistics. I am saying that women need to be told the benefits and the harms and they need to make their own decision."

Keen blasted the condescending attitude implicit in taking the decision of whether to screen out of the hands of the patients involved.

"You can use the word paternalistic, and that's what it is," he said. "We don't trust women to make their own decisions about whether to screen. We just tell them to screen. We just say mammography saves lives."

The researchers noted that mammograms may still provide benefits even to women whose lives they do not save, however.

"We have assumed that a 'life saved' means screening helps cure one woman with breast cancer who would otherwise have died from the disease without screening," they wrote. "However, all women with breast cancer may theoretically benefit from screening mammography through slowing the disease and therefore slightly prolonging their lives."