Screening mammography should be tossed out as an exercise that does more harm than good because it finds lesions that aren't clinically relevant and leads to radiation-linked deaths. Or, it is an essential part of preventive health, having reduced breast cancer mortality by 30% between 1990 and 2007.
Authors of three papers in the September issue of the journal Radiology are reigniting the conflict with contradictory reports, two of which advocate for the procedure, and one which suggests the practice may kill more women than it saves through secondary cancers and heart disease.
The controversy was provoked by one of the papers, which describes findings from a Swedish study of 133,065 women between the ages of 40 and 74 in two counties. The women were randomized into two groups, one of which was invited to mammographic screening, while the other, a control, received usual care. Both groups were followed for up to 29 years.
"There were 351 breast cancer deaths among the 77,080 subjects in the active study population group and 367 deaths among the 55,985 subjects in the passive study population group," wrote Stephen Duffy, professor of cancer screening at Queen Mary University of London, the lead author of the Swedish study with colleagues.
At 29 years of follow-up, the researchers determined that the number of women needed to undergo screening for seven years to prevent one breast cancer death was between 414 and 519, depending on the case status and cause of death source used.
"Most prevented breast cancer deaths would have occurred (in the absence of screening) after the first 10 years of follow-up."
The researchers said their findings confirm the 30% reduction in breast cancer mortality, and suggest more lives may be saved with longer follow-up. Also, they concluded that the absolute number of prevented breast cancer deaths observed rises with increasing time of follow-up.
The two other papers were invited commentaries on the Duffy research project.
In the first, Karsten Juhl Jorgensen, MD, John Keen, MD and Peter Gotzsche, MD of the Nordic Cochrane Center in Copenhagen and Department of Radiology of John H. Stroger, Jr. Hospital of Chicago, took strong objection to the findings, implying that mammographic radiologists are not doing the best thing for their patients.
They acknowledge that mortality has gone down, but argue that this is so because of improvements in treatment and in increased awareness, not because more destructive tumors are being caught earlier.
"Breast imagers, like other physicians, prefer to think that their daily activities improve health and save lives. However, the average breast imager could be doing more harm than good. During a 10-year period, starting in women aged 40, 50, and 60 years, an estimated 41%–46% of screening-detected breast cancers in the United States will represent overdiagnosis," they wrote.
Jorgensen and colleagues say that far too many women are receiving false positive results from mammograms. In fact, the risk of a false positive after 10 mammograms is 49%, they wrote. That means "19% of women who do not have breast cancer would have undergone biopsy after 10 mammograms."
They continued, "Substantial overdiagnosis and overtreatment increases mortality (e.g., from heart disease and lung cancer caused by radiation therapy). The net effect of screening on all-cause mortality, if any, must be minimal, even if screening still had some effect on breast cancer mortality today (which is doubtful.)"
In defense of the Swedish study's conclusions, however, Daniel B. Kopans, MD, of the Department of Radiology at Massachusetts General Hospital, Robert A. Smith of the American Cancer Society and Duffy wrote a rebuttal.
"The latest challenge to screening mammography has been the argument that screening leads to the diagnosis of a large number of breast cancers that, if left undiscovered, would never become clinically evident and thus would never become potentially lethal," Kopans and colleagues wrote.
They "recognize that there are almost certainly some breast cancers that will never be lethal," and that many women will be treated with systemic therapy without clinicians knowing specifically who will benefit and who won't.
But in conclusion, they wrote, "early detection, although not perfect, has been repeatedly demonstrated to reduce deaths from breast cancer and that the risk of overdiagnosis is small compared with this benefit."
Interviewed by phone, Stamatia Destounis, MD, managing partner of the Elizabeth Wende Breast Care in Rochester, NY, said she agrees with Kopans. "We can't live in that world where Dr. Jorgenson lives. The problem is that these early cancers, if left in the breast, no one knows the magical time they can turn into invasive cancer, or that they won't become a bigger or life-threatening problem down the line."
Destounis, a fellow with the American College of Radiology, said that to radiologists and clinicians, "The abnormality that may kill looks the same as the one that may wax and wane and do very little for years."
"We think mammography has helped reducing mortality by finding these small breast cancers that are very treatable," she said.