Effect of Three Decades of Screening Mammography on Breast-Cancer Incidence — NEJM
. . . this also reduces the dangers of over-diagnosis.
More after the break!
"By avoiding screening, women can reduce their risk of breast cancer by one third." From the letters appended to the article.
"There are two prerequisites for screening to reduce the rate of death from cancer.1,2 First, screening must advance the time of diagnosis of cancers that are destined to cause death. Second, early treatment of these cancers must confer some advantage over treatment at clinical presentation.
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In the United States, clinicians now have more than three decades of experience with the widespread use of screening mammography in women who are 40 years of age or older. We examined the temporal effects of mammography on the stage-specific incidence of breast cancer. Specifically, we quantified the expected increase in the incidence of early-stage cancer and determined the extent to which this has led to a corresponding decrease in the incidence of late-stage cancer."
The study relies on more three decades of data from the world's preeminent cancer surveillance program (SEER). What it shows is important because it is not what we have been led to believe.
Use of Screening Mammography and Incidence of Stage-Specific Breast Cancer in the United States, 1976–2008.
shows the substantial increase in the use of screening mammography during the 1980s and early 1990s among women 40 years of age or older in the United States. Figure 1A also shows that there was a substantial concomitant increase in the incidence of early-stage breast cancer among these women. In addition, a small decrease is evident in the incidence of late-stage breast cancer. As shown in Figure 1B, there was little change in breast-cancer incidence among women who generally did not have exposure to screening mammography — women younger than 40 years of age."
TABLE 1 shows the changes in the stage-specific annual incidence of breast cancer over the past three decades among women 40 years of age or older. The large increase in cases of early-stage cancer (from 112 to 234 cancers per 100,000 women — an absolute increase of 122 cancers per 100,000) reflects both detection of more cases of localized disease and the advent of the detection of DCIS (which was virtually not detected before mammography was available). The smaller decrease in cases of late-stage cancer (from 102 to 94 cases per 100,000 women — an absolute decrease of 8 cases per 100,000 women) largely reflects detection of fewer cases of regional disease. If a constant underlying disease burden is assumed, only 8 of the 122 additional early diagnoses were destined to progress to advanced disease, implying a detection of 114 excess cases per 100,000 women. Table 1 also shows the estimated number of women affected by these changes (after removal of the transient excess cases associated with hormone-replacement therapy). These estimates are shown in terms of both the surplus in diagnoses of early-stage breast cancers and the reduction in diagnoses of late-stage breast cancers — again, under the assumption of a constant underlying disease burden."
So, in localized breast cancers for every 100,000 women who undergo mammography screening, 8 will benefit, and 114 will be harmed. Remember the harms are significant. Simply being diagnosed with cancer causes harm, but the treatments are horrifying, including highly toxic poisons, radiation, surgery, and hormones.
There was no change at all in distant (metastasizing) cancers.
The study authors conclude:
"It does not involve a selected group of patients, a specific protocol, or a single point in time. Instead, it considers national data over a period of three decades and details what has actually happened since the introduction of screening mammography. There has been plenty of time for the surplus of diagnoses of early-stage cancer to translate into a reduction in diagnoses of late-stage cancer — thus eliminating concern about lead time.24 This broad view is the major strength of our study.
Our study raises serious questions about the value of screening mammography. It clarifies that the benefit of mortality reduction is probably smaller, and the harm of overdiagnosis probably larger, than has been previously recognized. And although no one can say with certainty which women have cancers that are overdiagnosed, there is certainty about what happens to them: they undergo surgery, radiation therapy, hormonal therapy for 5 years or more, chemotherapy, or (usually) a combination of these treatments for abnormalities that otherwise would not have caused illness. Proponents of screening should provide women with data from a randomized screening trial that reflects improvements in current therapy and includes strategies to mitigate overdiagnosis in the intervention group. Women should recognize that our study does not answer the question “Should I be screened for breast cancer?” However, they can rest assured that the question has more than one right answer."
Obviously, this is not the narrative we were supposed to find. That narrative was supposed to go something like this: For every 100,000 women screened by mammogram, 122 are diagnosed with cancer, and 114 of these benefit from the mammogram screening, leaving only 8 women who failed to respond to treatment. Of course, the results were the opposite with only 8 benefiting and 114 being harmed. As the authors note, the harm comes from biopsies, surgical interventions, radiation therapy, hormonal therapy, chemotherapy, and combination therapies all undertaken to treat imaging findings which would never have progressed to illness.
What makes this so damning is the fact that in myriad cancers, these findings hold. While we can spot many cancers early, and treat cancers, the results are frequently abysmal. Modern medicine came into being just after the turn of the 20th century, for it was then that a patient presenting to a doctor had a better than even chance of being helped by the treatments offered. Before that it was safer to not treat with a physician. That appeares to be where we are today in the treatment of many cancers, pre-20th century with the presentation for pre symptomatic cancer screening more injurious than beneficial.
It is very difficult to cut across the grain, and not participate in early cancer screening programs, but the more you know, the more likely you will be able to make informed decisions. There are no "correct" answers here, only informed decisions, and uninformed decisions. Choose to be informed.
H. Gilbert Welch Start with Overdiagnosed, and then keep reading. The life you save may be your own.