Can Mammograms Find the Right Breast Cancers Early?

FROM THE LECTURE SERIES: The Skeptic's Guide to Health, Medicine, and the Media

By Roy Benaroch, M.D., Emory University Affiliated Hospitals

Breast cancer is one of the most invasive cancers in women. The main question in this scenario is “Can mammograms find the right breast cancers early?” The emphasis here is on the ‘right cancers’—the ones that would cause grave harm if not detected in their early stage. It is imperative not just to detect the cancers early but to identify the correct ones.

Photograph of a doctor holding a mammogram film image.
Cancers detected through mammography screenings are mostly slow-growing cancers that probably would not have caused any harm. (Image: Chompoo Suriyo/Shutterstock)

Media’s Reaction to the American Cancer Society’s Guidelines

Popular media outlets such as The New York Times, CNN, and NBC raised concerns regarding the revised guidelines for mammograms by the American Cancer Society. In 2009, The New York Times ran a headline that read, “In Reversal, Panel Urges Mammograms at 50, not 40”. The CNN report stated, Task Force Opposes Routine Mammograms for Women Age 40–49, while NBC reported that “New Mammogram Advice Raises Worries”. A quote from the NBC article said that most women don’t need mammograms in their 40s and should get one every two years starting at 50. This was a surprising diversion from the American Cancer Society’s long-standing position, which was a universal recommendation for yearly mammograms starting at age 40.

Doctor assisting a woman to take her mammogram.
A potential drawback of mammography screening is ‘overdiagnosis’. (Image: antoniodiaz/Shutterstock)

The medical chief officer of the American Cancer Society unequivocally recommends mammography for women over 40 years. He criticized the new guideline by saying that mammography for women in their 40s saves lives, just not enough of them. However, the US Preventive Services Task Force (USPSTF) recommendations are not ever based on costs and do not include any assessment of a cost/benefit ratio. There are many instances where the media extensively criticized the USPSTF’s guidelines. A co-host of ABC’s daytime talk show, The View, claimed the government’s recommendations represent “gender genocide”. In another instance, a Washington Post columnist quoted that oncologists wanted to send members of the task force to prison, where they could “live out their years happily denying one another cancer screenings”.

Here, it is important to remember that the guidelines did not discourage women in their 40s from getting a mammogram. According to a quote in the story reported by CNN: “Before having a mammogram, women ages 40–49 should talk to their doctors about the risks and benefits of the test, and then decide if they want to be screened.” This quote from CNN’s story shows that shared decision-making based on evidence is a far cry from “gender genocide”.

This is a transcript from the video series The Skeptic’s Guide to Health, Medicine, and the Media. Watch it now, on The Great Courses Plus.

Illustration of the Impact of Mass Screening on Women at Different Ages

One of the best, most level-headed assessments of the 2009 recommendations was from The Atlantic in an article titled, “Rethinking the Mammogram Guidelines.” According to this article, even though it seemed like the change in recommendations was abrupt, research supporting changing the recommendations had been accumulating over years. One of the most influential studies combined five independent trials published by a Swedish group in 2002, seven years before the USPSTF’s recommendations changed. The Atlantic’s article simplified the comparisons to help the general readers make sense of the reasons behind the change. For instance, breast cancer screening advocates had been quoting a 9% reduction in cancer for screened women in their 40s, which although not big, is at least something. But the 9% change was a relative benefit, not an absolute change. In a larger group of women in the Swedish study, between the ages of 40 and 79, there was a 20% survival benefit seen in the screened population. That is, once again, a relative change.

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Findings of the Swedish Study

Photograph of a mammography machine in a hospital laboratory.
Research supporting the revised guidelines for mammograms published in 2009 had been accumulating for years. (Image: Yulia YasPe/Shutterstock)

The findings of the Swedish study suggest that out of 130,000 women screened annually for 15 years, 511 died, leaving the death rate at 0.4%. Among 117,000 non-screened women, 585 died, for a death rate of 0.5%. Even though there is a relative reduction of 20%, in terms of absolute numbers the difference is minimal. According to the calculations of one of the authors, on average, yearly mammograms for a woman in her 40s would statistically increase her lifespan by five days. This article also points out the comparison that five days is about equal to the fall in lifespan if someone rides a bike without a helmet for 15 hours. It also points out that in Sweden, where mammography has been widely used since 1990, the national breast cancer death rate had fallen by less than one death per 100,000 women. It must be kept in mind that there is genuine harm caused by mammography screening. There are cases of false positives, such as that 80% of women who undergo a breast biopsy based on mammography findings find out that they do not, in fact, have cancer. However, the bigger problem is that cancers detected through mammography screenings are mostly slow-growing cancers that probably would not have caused any harm.

The combined data from eight studies with 600,000 participants gives us a strong sample group. For 1,000 women aged 50 or older, four will die of breast cancer over the next 11 years, 22 of them will die of any kind of cancer, and about 100 will have a false alarm. Five of them will undergo intensive treatment for breast cancer that would never have hurt them, including surgery, chemo, and radiation therapy. If the same 1,000 women did not receive regular mammograms starting at age 50, there would be five deaths from breast cancer. But if all types of cancer are combined, the total deaths remain the same—22. Even if one death is saved from breast cancer, the overall cancer mortality will remain unchanged.

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Effects of Mammography on Mortality from Breast Cancer

According to a study in 2012, while the diagnosis of early breast cancer has doubled since mammography screening has become common, there has not been much of a decrease in the rate of advanced cancers found and treated. CSB stated the issue this way—“Mammograms lead to breast cancer ‘overdiagnosis’ in 1 million women.” A potential drawback of mammography screening is ‘overdiagnosis’. Overdiagnosing is not the same as misdiagnosing. The five women in the example of 1,000 screened women, based on their biopsies, indeed did have cancer. But these were not the right cancers and would not have caused any harm.

For breast cancers, population-based screening of everyone, regardless of their individual risks, is unlikely to have a big positive impact on overall survival. It is essential that media reinforces this message to move mindsets away from the overly simplistic messages that more screening is better, and all cancers are best caught early.

Common Questions About Breast Cancer

Q: What is the opinion of the medical chief officer of the American Cancer Society about mammograms?

The medical chief officer of the American Cancer Society unequivocally recommends mammography to women over 40 years of age.

Q: According to a co-host of ABC’s daytime talk show, The View, what does the US government’s mammography screening recommendations represent?

A co-host of ABC’s daytime talk show The View claimed the US government’s mammography screening represents “gender genocide”.

Q: What is the most level-headed assessment of the 2009 recommendations for mammography screening?

One of the best, most level-headed assessments of the 2009 recommendations was from The Atlantic in an article titled, “Rethinking the Mammogram Guidelines.”

Q: What is a major problem with cancers detected through mammography screenings?

Cancers detected through mammography screenings are mostly slow-growing cancers that probably would not have caused any harm.

Q: What is the potential drawback of mammography screening?

A potential drawback of mammography screening is ‘over-diagnosis’.

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