Health Letter, August 2016
By Azza AbuDagga, M.H.A., Ph.D.
Breast cancer is the second most common cancer among American women, with nearly a quarter of a million women newly diagnosed with the disease each year. Yet deaths related to breast cancer have declined substantially since the 1970s, due, in part, to improved detection methods and treatment.
Screening for breast cancer means looking for signs of the disease in symptom-free women at a certain age or with specific risk factors, with the goal of catching and treating the disease early. This screening is done mostly by mammograms (x-ray exams of the breast).
There has been a long-standing uncertainty about the benefits and harms of mammograms among various age groups. This has led to various organizations issuing different — sometimes conflicting — screening guidelines over the years.
The U.S. Preventive Services Task Force (USPSTF), a volunteer panel of experts working independently of the drug and medical device industries, recently released a new set of breast cancer screening guidelines for primary care providers to use in counseling women about breast cancer prevention. These guidelines apply to women with average breast cancer risk, defined as those 40 years of age or older with no known physical signs or symptoms of breast abnormalities, pre-existing breast cancer or high-risk breast lesions; no genetic conditions associated with breast cancer; and no history of large doses of chest radiation before the age of 30.
After a period of public comments on the draft guidelines in 2015, the final guidelines were released on the USPSTF’s website in January 2016. They were subsequently published in the February issue of Annals of Internal Medicine.
Balancing the benefits and risks of mammograms
The USPSTF based its new recommendations on an extensive analysis of the evidence on the effect of mammography screening on breast cancer deaths. This analysis showed that benefits of regular mammograms (mainly avoiding breast cancer deaths) increase with age, although this relationship does not start abruptly at any particular age. It found that screening 10,000 women from 60 to 69 years of age was linked to 21 fewer breast cancer deaths over a 10-year period. The benefit was smaller in younger women: screening 10,000 women from 50 to 59 years of age was linked to eight fewer breast cancer deaths, and screening 10,000 women from 40 to 49 years of age was linked to only three fewer breast cancer deaths.
In contrast to the benefit increasing with age, USPSTF’s analysis found that the harms of mammograms either remain constant or decrease with age. These harms include false-positive results, mammograms that falsely suggest breast cancer. Such incorrect results can lead to psychological distress, as well as unnecessary breast biopsies and other procedures.
Another major harm associated with mammograms is overdiagnosis: the detection and treatment of breast cancer that would never have been detected or progressed to threaten the health of the woman were it not for the screening. Estimates suggest that one in five women diagnosed with breast cancer over 10 years will experience overdiagnosis related to mammograms.
The mammography recommendations
The updated USPSTF guidelines concluded that the balance between the benefits and harms of screening for breast cancer with mammograms becomes more favorable with increasing age. As summarized in the table below, the benefits of mammograms outweigh their harms in average-risk women ages 50 to 74, with the greatest benefit occurring in women in their sixties. With this finding in mind, the USPSTF recommends that average-risk women ages 50 to 74 get mammograms every two years.
The USPSTF also determined that the current evidence is insufficient to assess the balance of the benefits and harms of mammograms in women 75 and older. Therefore, the task force does not make a recommendation regarding mammograms for women in this age group.
Based on its conclusion that the benefits of mammograms outweigh their harms by only a small degree for women in their forties, the USPSTF recommends that these women make decisions about screening according to their individual values and preferences. So a woman who values the possible benefit of mammograms over their harms can make an informed decision to begin her first mammogram in her forties. Conversely, a woman who is more concerned about the potential harms of mammograms may wish to delay her first mammogram until she reaches 50.
Nonetheless, the USPSTF cautions that as women advance through their forties, the incidence of breast cancer rises. Therefore, women in their late forties will likely benefit more from mammograms than would women in their early forties.
|40-49 years||The decision to start screening mammography in women in this age group should be an individual one. Women who place a higher value on the potential benefit than the potential harms may choose to begin screening every two years between the ages of 40 and 49 years.|
|50-74 years||Routine screening every two years|
|75 years or older||No recommendation due to insufficient evidence of the balance of benefits and harms.|
Source: U.S. Preventive Services Task Force, 2016.
Recommendations by other organizations
Several organizations that have a stake in breast cancer screening took various stands in response to the USPSTF guidelines. The American College of Obstetrics and Gynecologists, the American College of Radiology (ACR) and the Society of Breast Imaging (SBI) issued statements that they will continue to recommend annual routine mammograms for women starting at the age of 40. Unlike the USPSTF, these organizations did not base their extended recommendations on the most recent evidence.
On the other hand, the American Cancer Society (ACS), an influential voice in cancer policy and care in the U.S., released its own guidelines in 2015. The ACS recommends starting breast cancer screening in average-risk women at age 45. It also recommends routine mammograms every year in women 45 to 54, and every other year among those over 55 as long as they have a life expectancy of at least 10 years. However, the research analysis supporting the ACS recommendations was conducted by researchers who had financial ties to the industry and were likely biased in favor of more screening.
What women should do
The new USPSTF guidelines currently offer the best evidence-based recommendations for mammogram screening in average-risk women. Women should discuss their personal mammogram preferences with their physicians. Average-risk women under 50 should consider their personal views of the benefits and harms of mammograms when considering routine screenings.
Women at high risk for breast cancer, particularly those with family histories of breast cancer, should discuss with their physician or other health care professional the ideal time to start breast cancer screening.
 Centers for Disease Control and Prevention. Breast cancer statistics. https://www.cdc.gov/cancer/breast/statistics/. Accessed June 27, 2016.
 Berry DA, Cronin KA, Plevritis SK, et al.; Cancer Intervention and Surveillance Modeling Network (CISNET) Collaborators. Effect of screening and adjuvant therapy on mortality from breast cancer. N Engl J Med. 2005;353(17):1784-1792.
 Nelson HD, Fu R, Cantor A, et al. Effectiveness of breast cancer screening: Systematic review and meta-analysis to update the 2009 U.S. Preventive Services Task Force recommendation. Ann Intern Med. 2016;164(4):244-255.
 Nelson HD, Fu R, Cantor A, Pappas M, Daeges M, Humphrey L. Effectiveness of breast cancer screening: Systematic review and meta-analysis to update the 2009 U.S. Preventive Services Task Force recommendation. Ann Intern Med. 2016;164(4):244-255.
 American Congress of Obstetricians and Gynecologists. ACOG statement on revised American Cancer Society recommendations on breast cancer screening. October 20, 2015. http://www.acog.org/About-ACOG/News-Room/Statements/2015/ACOG- Statement-on-Recommendations-on-Breast-Cancer-Screening. Accessed June 24, 2016.
 American College of Radiology. News Release: ACR and SBI continue to recommend regular mammography starting at age 40. October 20, 2015. http://www.acr.org/About-Us/Media-Center/Press-Releases/2015-Press-Releases/20151020- ACR-SBI-Recommend-Mammography-at-Age-40. Accessed June 24, 2016.