More than half of breast cancers newly diagnosed in the United States are likely cases of mistaken identity that subject women to needless anxiety, treatment and expense, researchers reported Wednesday in the New England Journal of Medicine.
The study also found that the value of mammograms as a life-saving tool has been significantly overstated. Instead, the introduction of more effective treatments should get most of the credit for improving survival rates among women diagnosed with breast cancer, the researchers concluded.
The findings cast fresh doubt on the value of universal breast cancer screening for women over 40 with no family history of the disease. They also underscore that breast cancer — the most common form of cancer among American women — is a far more complex disease than initially believed.
The hope that early detection would consistently save women’s lives accorded with scientists’ limited understanding of cancer in the mid-1970s. Experts believed that a small breast lump was almost always a harbinger of a tumor that would, with time, grow and spread.
Catch and treat it early, their reasoning went, and you will see one less woman coming in later with a large and aggressive cancer.
But medical researchers have come to recognize that a tumor’s genetic make-up, as well as the interaction between tumor and host, are better predictors of its progression than the tumor’s size upon discovery. One woman’s tumor might reach 2 centimeters and then stop growing for many years. Another’s might progress from undetectable to a dangerous 5 centimeters in a matter of months.
It was a new, more complex picture of breast cancer. And it undercut the idea that early detection and early treatment were essential to save lives.
“The mantras, ‘All cancers are life-threatening’ and ‘When in doubt, cut it out,’ require revision,” Dr. Joann G. Elmore, a physician and epidemiologist at the University of Washington, wrote in an editorial that accompanies the study. The “well intentioned efforts” of doctors, she wrote, are exacting “collateral damage.”
As breast imaging became widely available in the early 1980s, physicians told women that catching tumors early, before they could be felt by hand, was key to their survival.
Advocates quickly began pushing for universal screening programs. By the mid-1980s, an American Cancer Society awareness campaign told women over 35, “If you haven’t had a mammogram, you need more than your breasts examined.”
It’s now clear that physicians, activists and the media “quite simply have overstated the value” of mammography, said study leader Dr. H. Gilbert Welch, one of the first researchers to raise questions about overscreening.
Whether motivated by true belief, commercial gain or fear of litigation, he said, those forces have been slow to accept that when all women get mammograms, some will respond to scary findings in ways that do more harm than good.
In 2016, physicians in the United States are expected to diagnose 246,660 new cases of invasive breast cancer, along with 61,000 new cases of non-invasive breast cancer (sometimes referred to as ductal carcinoma in situ, or DCIS).
The analysis of data from the National Cancer Institute suggests that the majority of abnormalities picked up by screening mammograms would likely never become deadly if left alone. Still, patients and their physicians routinely attack small lump with biopsies, diagnostic work-ups and treatments that can be risky and debilitating.
Welch, who teaches community and family medicine at Dartmouth University’s Geisel School of Medicine, and his team tallied the number of breast cancer findings and the size of the tumors found in women over 40 who were diagnosed with breast cancer between 1975 and 1979, before screening mammography became widely available.
They compared those figures with breast cancer findings between 2000 and 2002, when screening was widespread.
For both groups, they tracked how women were treated and whether they were still alive 10 years after diagnosis.
The team observed that as more women got routine mammograms, more breast cancers were diagnosed. The additional cancers tended to be smaller, or to be confined to spaces, such as milk ducts, where they had not invaded normal tissue.
If catching tumors while they were still small were a way of nipping large, aggressive tumors in the bud, then widespread screening should have reduced the number of large tumors discovered on mammograms. But the rate at which large and aggressive tumors were found remained “essentially unchanged” between 1975 and 2010, the researchers found.
“The introduction of screening mammography has produced a mixture of effects,” the authors explained. To a modest extent, mammography screening was having the desired effect of finding dangerous tumors before they had grown large. For those women — estimated to be about 20% of those whose small tumors were detected by screening mammography — early treatment was potentially life-saving.
But the other 80% of women likely would not have died of breast cancer had their tumors never been detected in the first place.
Ironically, as mammography became more widespread and technically better, screening was doing a better and better job of finding these harmless tumors: while lumps smaller than 2 centimeters represented 37% of mammogram-detected abnormalities in the early years of the study, they represented 67% of a much larger pool by 2010.
By comparing changes in mortality rates over time for women diagnosed with tumors of various sizes, the researchers calculated that improvements in breast cancer therapy were responsible for at least two-thirds of the reduction in deaths, according to the study.
Dr. Michael LeFevre, a University of Missouri physician who was not involved in the new study, said while the findings offer only rough estimates of mammograms’ harms, it helps counter a powerful narrative about routine breast cancer screening for all women.
“When a woman is diagnosed with breast cancer and survives, she instinctively believes that the mammogram ‘saved her life,’” said LeFevre, a member of a federal task force that recommended more targeted mammography screening for women. More likely, he said, it has upended her life without prolonging it and it’s time for physicians to help their patients understand that.
UCLA breast cancer specialist Dr. Patricia Ganz said the study was a useful reminder that “if we just keep doing what we’ve been doing, we’re exposing lots of people to treatment they don’t need or can’t afford.”
At the same time, she said she understands patients’ — and physicians’ — impulse to act.
“People don’t want to regret” their responses to a frightening finding on a mammogram, said Ganz, an oncologist at UCLA’s Jonsson Comprehensive Cancer Center. But the truth is, “any activity we do in healthcare has the potential to do harm. You just always hope that the benefits will outweigh the harms.”
Welch acknowledged that the new findings will do little to clarify who should get mammograms, and how often.
But they should prompt patients and their doctors to consider that aggressive treatment of a small lump will not always lead to better health. Women should know that just as with prostate and lung cancer, deferring treatment until a tumor reveals its aggressive nature “is a choice,” he said.
And because small lumps are almost exclusively found on mammograms, the study is an important reminder that “indiscriminate testing can be a recipe for being made sick,” he added.
MORE IN SCIENCE