Susan G. Komen for the Cure’s 2011 breast cancer awareness campaign has come under fire as a misleading overstatement of the benefits of mammography which ignore its potential harms in a commentary published Aug. 3 the British Medical Journal.
Lisa Schwartz, MD, and Steven Woloshin, MD, of the Center for Medicine and the Media at the Dartmouth Institute for Health Policy and Clinical Practice, in Lebanon, N.H., wrote, “There is a big mismatch between the strength of evidence in support of screening and the strength of Komen’s advocacy for it.”
Schwartz and Woloshin referred to growing evidence that screening mammography reduces a woman’s chance of death by a small amount, but also is linked with harms.
The authors took issue with Komen’s claims that the five-year survival rate for breast cancer when detected early is 98 percent. They placed the rate at 23 percent.
They cited the lead time bias and overdiagnosis as contributing to the confusion.
Five-year survival rates reflect the proportion of women alive five years after diagnosis. However, when women are diagnosed earlier, as via screening mammography, five-year survival appears higher, than among women who were diagnosed later in the course of disease, as via a palpable mass.
The second issue, according to Schwartz and Woloshin, is overdiagnosis. That is, screening mammography will detect some cancers that do not progress. “Overdiagnosis distorts survival statistics because the numerator and denominator now include people who have a diagnosis of cancer but who, by definition, would survive the cancer.” These women also face the harms of treatment—surgery, radiation therapy and chemotherapy.
Survival statistics are complex and confusing. Schwartz and Woloshin characterize them as meaningless in the context of screening, and wrote, “There is no correlation between changes in survival and what really matters, changes in how many people die.” Even primary care physicians misinterpret improved survival as evidence that screening save lives, according to the authors.
According to Schwartz and Woloshin, the statistic that matters is not five-year survival but the actual benefit of mammography—“a reduction in the chance that a women in her 50s will die from breast cancer over the next 10 years from 0.53 percent to 0.46 percent, a difference of 0.07 percentage points.”
The authors concluded by stressing that women need facts. In contrast, Susan G. Komen “undermined decision making by misusing statistics to generate false hope about the benefits of screening.”
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