A provocative article appearing in the latest edition of the Archives of Internal Medicine examines this claim and concludes that the ability of routine screening to prevent women from dying of breast cancer has been overstated.
The authors’ rather startling summary: “Most women with screen-detected breast cancer have not had their life saved by screening. They are instead either diagnosed early (with no effect on their mortality) or overdiagnosed.”
This is not a message most of us are accustomed to hearing. The benefits of routine screening for breast cancer have been drilled into virtually every American woman over the age of 20 or thereabouts, and reinforced with numerous, emotionally powerful stories of individual women whose cancer was detected during a regularly scheduled mammogram and who are alive to tell about it.
The article’s authors used DevCan, a software program developed by the National Cancer Institute for analyzing SEER )Surveillance Epidemiology and End Results) data to estimate women’s 10-year risk of a breast cancer diagnosis and 20-year risk of death. They crunched the numbers in several different ways: with mammography, without mammography, with varying statistical assumptions about risk reduction in breast cancer deaths, and for women at ages 40, 50, 60 and 70.
Their analysis found that among all age groups, fewer than 25 percent of women likely had their lives saved because of a screening mammogram. In many cases, the authors explained, “a woman may have had her breast cancer detected early yet not benefit from early detection because her cancer would have been equally treatable had it presented clinically… Alternatively, a woman may have been overdiagnosed – diagnosed with a cancer not destined to cause symptoms or death.”
There’s a caveat to this analysis. It’s based on a set of statistical assumptions rather than an actual group of women, hence comes with several limitations.
Nevertheless, it challenges the accuracy of one of the most widely held notions about screening and prevention: that women can reduce their risk of dying of breast cancer by having regular mammograms – and, conversely, that women who skip getting a mammogram are somehow irresponsible or are putting themselves at undue risk.
Screening and prevention in fact are not the same thing, a distinction that seems to have become lost in many of the public health messages, particularly when it comes to cancer. Nor does screening necessarily guarantee a good outcome; individual tumor biology seems to be the most critical determinant of whether a cancer will be slow-growing or metastasizing, whether it will respond well to treatment or become treatment-resistant.
It’s only been in the last few years that the public discussion has become more nuanced about the benefits of screening and early detection. For instance, health experts have backed away from routine screening for prostate cancer, citing the unreliability of the PSA test and the risk of overdiagnosis and overtreatment. Two years ago the U.S. Preventive Services Task Force recommended against routine mammograms for women in their 40s, citing the lack of a clear life-saving benefit and calling instead for this to be an individual decision between these women and their doctors.
This is an emotional issue for many people, though, and the authors of the Archives of Internal Medicine acknowledge the difficulty of squaring the science with women’s personal experiences:
Today, more people are likely to know a cancer survivor than ever before. Between 1971 and 2007, the number of cancer survivors in the United States more than doubled, from 1.5% to 4.0% of the population. Breast cancer survivors are particularly common: they now represent approximately 2.5 million, or one-fifth of the current survivor population.
Earlier diagnosis (either via enhanced awareness or screening) and better treatment are clearly part of the explanation for this large survivor population. But so too is the enthusiasm for screening and the resulting overdiagnosis. And, ironically, this enthusiasm may, in turn, be the product of a large number of survivors. This self-reinforcing cycle (the more detection, the more enthusiasm — the so-called popularity paradox of screening) is driven, in part, by the presumption that every screen-detected breast cancer survivor has had her “life saved” because of screening. Our analyses suggest this is an exaggeration. In fact, a woman with screen-detected cancer is considerably more likely not to have benefited from screening. We believe that this information is important to put cancer survivor stories in their proper context.
Importantly, no one is saying screening is worthless or that we should all stop doing it. By the researchers’ own estimates, mammography does help save lives up to 25 percent of the time. But it seems to be a matter of recognizing that mammograms aren’t the silver bullet we’d like them to be, Dr. Susan Love writes in a column that appeared earlier this month at AOL Healthy Living.
When it comes to screening mammograms, we tend to engage in wishful thinking and ignore the science, she wrote. “We get angry at the experts who tell us studies show that mammography is less beneficial for women in their 40s. We focus on the idea that if only women had regular mammograms every cancer would be found early and cured.”
Rather than argue about screening guidelines, Dr. Love writes, “we need to face the science squarely and focus on prevention, so that we can learn how to avoid cancer in the first place.”
West Central Tribune file photo