Research stirs debate on mammography

Research stirs debate on mammography

The role of screenings in the early detection of breast cancer is in the media spotlight again as results of a new study indicate that annual mammography in women ages 40-59 does not reduce mortality from breast cancer beyond that of physical examination or usual care when adjuvant therapy for breast cancer is freely available.¹

In 1980, the Canadian National Breast Screening Study was initiated by researchers as a randomized controlled trial of screening mammography and physical examination of breasts in 89,835 women, ages 40 to 59. The new report updates findings based on up to 25 years (mean 22 years) follow-up. All women participating in the study underwent an initial clinical breast examination at the screening center by nurses or physicians. Women ages 40-49 were randomized to baseline and four additional annual mammograms, or no mammography (usual care with their family physician). Women ages 50-59 were randomized to annual breast examinations at the study center with or without baseline and four additional annual mammograms.

The analysis shows 1,190 breast cancers were diagnosed; 666 occurred in women who had mammograms, and 524 occurred in the control group. However, after 25 years, nearly the same amount of women in each group had died from the disease. The analysis also indicates that 22% of invasive breast cancers detected in the arm of the study in which women received mammography were overdiagnosed, which caused women to undergo unnecessary procedures for cancers that were slow-growing or did not require treatment.¹

Guidance to change?

In November 2009, the U.S. Preventive Services Task Force (USPSTF) recommended against routine screening mammography for women ages 40-49 and advised biennial rather than annual screening for women ages 50-74.² The group updated its guidance in December 2009 to state, "The decision to start regular, biennial screening mammography before the age of 50 years should be an individual one and take patient context into account, including the patient’s values regarding specific benefits and harms." (See the Contraceptive Technology Update article, "Check the new screening guidance for cervical cancer and breast cancer," January 2010, p. 1.)

The American College of Obstetricians and Gynecologists (ACOG) issued guidelines in 2011 that call for mammography screening be offered annually to women beginning at age 40.³ (See "New guidance issued for breast screening, CTU, October 2011, p.116.) ACOG continues to stand by its 2011 guidance in light of the new evidence, as does the American Cancer Society, which has issued similar recommendations.

What’s your stance?

When the USPSTF issued its 2009 recommendations, its rationale was based on that for women ages 40-49 years who are at relatively low risk for breast cancer, annual mammograms might lead to false positive results that result in psychological harms, unnecessary imaging tests, and biopsies in women without cancer. As for women ages 50 to 74 years, too-frequent screening could lead to overdiagnosis.⁴

An important point made by the current research was the harm done to women by mammographic screening, notes Anita Nelson, MD, professor in the Obstetrics and Gynecology Department at the David Geffen School of Medicine at the University of California in Los Angeles. In the current study, 22% (106/484) of mammography-detected invasive breast cancers were over-diagnosed, which represented one over-diagnosed breast cancer for every 424 women who received mammography screening in the trial.¹

The current study’s findings regarding lack of efficacy of screening mammograms and overdiagnosis are comparable to other recent studies assessing breast cancer screening,^5,6 notes Andrew Kaunitz, MD, professor and associate chair in the Obstetrics and Gynecology Department at the University of Florida College of Medicine — Jacksonville. Annual mammography screens have become an easy recommendation for clinicians to make, while for patients, the reassurance that accompanies a normal mammogram is comforting, observes Kaunitz. While many patients will be perplexed by information from the new study, others might view it with suspicion, he notes.

"While we await updated guidance from professional societies, my approach is to encourage patients to follow the 2009 US Preventive Service Task Force guidelines: Start at age 50 in average risk women, and screen every two years," states Kaunitz.

REFERENCES

1. Miller AB, Wall C, Baines CJ, et al. Twenty five year follow-up for breast cancer incidence and mortality of the Canadian National Breast Screening Study: randomised screening trial. BMJ 2014; doi: 10.1136/bmj.g366.
2. U.S. Preventive Services Task Force. Screening for breast cancer: U.S. Preventive Services Task Force recommendation statement. Ann Intern Med 2009; 151:716-726.
3. American College of Obstetricians and Gynecologists. ACOG practice bulletin. Breast cancer screening. Practice Bulletin #122. Obstet Gynecol 2011; 118(2 Pt. 1):372-382.
4. Mitka M. Physicians, patients not following advice from USPSTF on mammography screening. JAMA 2013; 309(20):2,084.
5. Kalager M, Zelen M, Langmark F, et al. Effect of screening mammography on breast-cancer mortality in Norway. N Engl J Med 2010; 363(13):1,203-1,210.
6. Autier P, Boniol M, Gavin A, et al. Breast cancer mortality in neighbouring European countries with different levels of screening but similar access to treatment: trend analysis of WHO mortality database. BMJ 2011; 343:d4411.