(NaturalNews) 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."
Yet the procedures also carry risks. Mammograms may result in "false positives," leading healthy women to undergo traumatic biopsies or even cancer treatment. In other cases, non-aggressive cancers may still be treated aggressively, leading to breast removal or severe side effects from drug and radiation therapy.
"Insurance companies and patients alike must pay for these tests," Kane said. "They are buying something. I just want to tell them what they are buying."
Other researchers have raised concerns that the radiation exposure women undergo during mammograms may actually raise their risk of breast or other cancers. Concern over unnecessary radiation exposure is the reason that doctors do not recommend mammograms for most women under the age of 40, in whom breast cancer risk tends to be low.
In addition, some health professionals warn that the compaction experienced by the breast during screening may rupture blood vessels and cause cancers to spread to other parts of the body.
Screening advocates disputed the study's findings with numbers of their own. According to Julietta Patnick, director of cancer screening programs for the United Kingdom's National Health Service, an independent review panel has concluded that screening in the United Kingdom saves one life for every 8 cancers detected. Robert Smith, director of cancer screening for the American Cancer Society, said that over the course of 20 years, one life could be saved by screening 465 women for 7 years each.
The new study is not the first to call the effectiveness of mammography into question, however. A 2001 study known as the Cochrane analysis found that while one life would be saved if 2,000 women underwent regular screening for 10 years, another 10 women would undergo unnecessary treatment such as surgery or radiation. They noted that it was difficult to determine which cancers would have led to death or even symptoms in the absence of treatment. The researchers concluded that it is "not clear whether screening does more harm than good."
The Cochrane analysis reviewed seven different studies including a total of 500,000 women.