“If you are a woman over 35, be sure to schedule a mammogram. Unless you’re still not convinced of its importance. In which case, you may need more than your breasts examined.” —From an old American Cancer Society Poster
For every 1000 women aged 40 to 74 years who participated in screening, 3.9 diagnosed with breast cancer died compared with 5.0 among those who did not participate. The absolute benefit in terms of reduced deaths due to mammography screening, therefore, is about one in 1000.
This may not come as a surprise to women's health experts. Patients are another story.
In a survey of more than 10,000 people in nine European countries, researchers at the Max Planck Institute for Human Development in Berlin found that 92% of women reported they either did not know how much mammography reduces mortality or they vastly overestimated the benefit, believing the benefit to be one in a hundred rather than one in a thousand. Many thought the benefit was even greater.
The results, published online Aug. 12 in the Journal of the National Cancer Institute, showed that more than 40% of women surveyed in France, the Netherlands, and the U.K. believed the reduction in mortality was one in 10 or even one in 5.
This kind of faith in cancer screening is not restricted to women and mammography. The researchers found that 89% of men quizzed about the benefits of screening for prostate-specific antigen overestimated the benefit by as much as women did for mammography.
The problem stems from the widespread campaigns, particularly in Western nations, aimed at increasing participation in screening programs. These campaigns try to persuade not through reasonable arguments but with emotional ones.
When considering that mammography uses ionizing radiation and that multiple exposures over extended periods of time carry long-term risks of cancer, the inability of patients to properly assess the benefits of this exposure raises questions about whether they can provide informed consent. Adding to the downside for both mammography and PSA screening is the harm that may come from false positives that lead to unnecessary invasive follow-up procedures, such as biopsy and treatment.
In an editorial accompanying the research results, Drs. Lisa M. Schwartz and Steven Woloshin of the Dartmouth Institute for Health Policy and Clinical Practice in Hanover, NH, suggested that messages promoting the use of screening should be based on facts. In the context of results citing the lower than widely believed benefits from prostate and breast cancer screening, they noted that prostate screening leads to overdiagnosis of between 10 and 30 patients for every 1000 screened and to unnecessary biopsy from false-positive mammograms in 50 to 200 of every 1000 women screened.
Schwartz, a Dartmouth associate professor of medicine and community and family medicine, told Oncology News International that screening advocates should describe the benefits as well as the risks associated with overdiagnosis and overtreatment.
"I think they should say something like: ‘Mammograms (PSA tests) have been shown to lower the chance of dying from breast cancer (prostate cancer). But (these tests) also have harms. We'll give you the information about the benefits and the harms so you can make a decision that is right for you.'"
Doing so would mark a quantum shift in screening advocacy. Decades of ad campaigns designed to increase the number of women participating in routine mammography, for example, have created the perception of mammography as a powerful tool for reducing deaths from breast cancer. In their JNCI editorial, Schwartz and Woloshin state that "selling screening can be easy. Induce fear by exaggerating risk. Offer hope by exaggerating the benefit of screening. And don't mention harms."
But is this how healthcare should be practiced? Not according to Schwartz and Woloshin: "We need to move from selling screening to helping people realize that screening is a genuine choice. That means routinely giving people the information needed to make these choices."
