Breast Cancer Screening: The Evidence is Piling Up

Kenneth W. Lin, MD, MPH


October 26, 2015

Editorial Collaboration

Medscape &

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Hi, everyone. I'm Dr Kenny Lin. I am a family physician at Georgetown University School of Medicine, and I blog at Common Sense Family Doctor.

Six years ago, at the height of the Congressional debate over the polarizing health reform law that would eventually be known as the Affordable Care Act, the US Preventive Services Task Force (USPSTF) released new breast cancer screening recommendations[1] that diverged from previous guidelines by starting routine mammography at age 50 years, rather than 40, and recommending screening every 2 years instead of annually. It also found insufficient evidence to support the practice of clinical breast examination in women without breast symptoms, and recommended against teaching women breast self-examination. (Full disclosure: I was a staffer for the USPSTF when these recommendations came out, but was not involved in authoring or approving them for publication.)

The Task Force at that time had no regulatory authority to mandate public or private insurance coverage for preventive services, and it preserved the option for women to begin screening mammography at any point after age 40 years if they so desired. Nonetheless, its guideline was widely criticized, and subsequent studies have shown that it had little effect on clinical practice.

Now, the American Cancer Society (ACS), which was among the USPSTF's critics in 2009, has published an update to its guideline[2] on breast cancer screening for women at average risk. After reviewing evidence from older randomized trials and more recent observational studies of screening mammography, the ACS decided to raise the age to begin routine screening from 40 to 45 years and recommends screening women every other year after age 55 years. Finally, they went even further than the USPSTF by advising against performing clinical breast examination for the purpose of breast cancer screening in women of any age.

Although some differences remain between the ACS's new guideline and those of the USPSTF, which are also being updated, they agree on several important points. First, both guidelines emphasize that the benefits and harms of screening mammography are close enough in younger women that the decision to screen should not be reflexive, but rather a shared decision that reflects a patient's preferences and values. Second, both guidelines mention overdiagnosis of breast cancer as a significant harm of screening, even though its magnitude is difficult to estimate precisely.

Finally, both guidelines recognize that the clinical breast examination provides limited value in women who are already being screened with mammography. Specifically, the ACS concluded that the clinical examination increases false-positive rates without improving cancer outcomes.

I think that this last point may be the most challenging for clinicians to accept. Many of my colleagues will surely come forward with stories about patients in whom a routine clinical breast examination revealed an abnormality that turned out to be cancer and saved someone's life. And how can we possibly prevent suffering and death from breast cancer if we don't look for it, or look for it less often?

Keep in mind, though, that the plural of "anecdote" is not "evidence." Statistically, approximately 13% of breast cancers found on screening mammography actually result in a life saved.[3] Unfortunately, the remainder will be fatal regardless of treatment, or would have been equally curable if detected at a later clinical stage.

And we should not forget the big picture: Preventing breast cancer deaths is not the only outcome of breast cancer screening. Women develop breast cancer in their 20s and 30s, too, and some breast cancers progress so rapidly in older women that a 1-year screening interval is not close enough to catch them. So why don't we try to save more lives by starting screening at age 20 and repeating the test multiple times each year? Cost considerations and radiation exposure aside, this strategy would lead to far more harm than good because it would result in a staggeringly high rate of false-positive results, anxiety, biopsies, and unnecessary treatments.

I hope that the ACS's new breast cancer screening guideline persuades many family physicians to change their practices. Change can be hard, but this sound, evidence-based guideline reflects the best science on the benefits and limitations of clinical breast examinations and screening mammography.

This has been Dr Kenny Lin for Medscape Family Medicine. Thank you for listening.


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