Breast cancer is the second most common cause of cancer death in US women,1,2 and screening mammography has been shown to decrease mortality.3,4 But the age at which to start screening, the intervals between mammograms, and the extent of the benefits (and harmful effects) of mammography are still hotly debated.
The clash between those who favor greater use of mammography and those who prefer less frequent and delayed screening heated up in July, when the American College of Obstetricians and Gynecologists (ACOG) released its new breast cancer screening guidelines.5 ACOG now recommends annual mammography starting at age 40; its previous guidelines called for mammograms every 1 to 2 years for women in their 40s and annual screening beginning at age 50.5
The US Preventive Services Task Force (USPSTF) issued updated breast cancer screening guidelines in November 2009 (TABLE 1).5,6 The new guidelines oppose routine screening for women ages 40 to 49 and recommend biennial, rather than annual, mammography for women ages 50 through 74. The decision to initiate screening before age 50 should be an individual one, based on the patient’s values as well as her individual risk factors, the USPSTF maintains. The Task Force, which previously recommended mammography every 1 to 2 years for all women ages 40 and older, does not recommend breast self-examination and finds insufficient evidence to assess the benefits of clinical breast exams.7
Both organizations have prominent medical groups in their camp: The American Cancer Society, National Comprehensive Cancer Network, American College of Surgeons, and American College of Radiology, among others, echo ACOG’s call for annual screening starting at age 40, while the American Academy of Family Physicians, American College of Physicians, National Breast Cancer Coalition, and World Health Organization (WHO) support the USPSTF’s position.8-10
Where does this leave you and your female patients? A look at the rationale behind these divergent recommendations and the latest evidence of the benefits and risks associated with screening mammography will help you cut through the controversy.
TABLE 1
Breast cancer screening: Divergent views5,6
| Organization | Age (years) | BSE | CBE | Mammography |
|---|---|---|---|---|
| ACOG | ≥40 | Encourages breast self-awareness | Annually | Annually |
| USPSTF | 40-49 50-74 | Recommends against teaching (D) | Insufficient evidence (I) | Not routinely recommended (C) Every 2 y (B) |
| USPSTF grades | ||||
| A: Recommended (high certainty of substantial benefit) | ||||
| B: Recommended (moderate or high certainty of moderate benefit or moderate certainty of substantial benefit) | ||||
| C: Not routinely recommended (at least moderate certainty that benefit is small) | ||||
| D: Not recommended (moderate or high certainty of no benefit or that harms outweigh benefits) | ||||
| I: Evidence is insufficient to assess benefits and harms | ||||
| ACOG, American College of Obstetricians and Gynecologists; BSE, breast self-examination; CBE, clinical breast examination; USPSTF, United States Preventive Services Task Force. Source: USPSTF. Grade definitions. May 2008. Available at: http://www.uspreventiveservicestaskforce.org/uspstf/grades.htm. Accessed August 19, 2011. | ||||
Same facts, different conclusions
The recommendations of the USPSTF are based on a systematic review of randomized clinical trials and data from the Cancer Intervention and Surveillance Modeling Network (CISNET) that allowed the researchers to assess various screening parameters.6,8,11 ACOG, too, based its guidelines on an evidence review,12 including the same data used by the USPSTF. Each organization interpreted the findings differently, however, particularly with regard to the benefits and potential harms associated with screening mammography.
The USPSTF points out that screening leads to the greatest absolute reduction in breast cancer mortality in women older than 50. For women ages 39 to 49, the USPSTF analysis revealed, it would take 1904 mammograms to prevent one breast cancer death. For women ages 50 to 59, the number of mammograms needed to prevent a single breast cancer death is 1339; and for women in their 60s, the number needed to screen is just 377.8
The USPSTF notes that false-positive results can lead to additional medical visits and unnecessary treatment, as well as potential psychological harm.7,8
ACOG focused more on cancer growth. Although women in their 40s have a lower probability of breast cancer (1 in 69) than their older counterparts (1 in 42 for women in their 50s and 1 in 29 for women in their 60s) (TABLE 2),2,5,8,12 tumors tend to grow faster in the younger women. That fact played a key role in shaping ACOG’s new guidelines. The average “sojourn time” (the interval between the time a breast tumor can be detected by mammogram and the time at which it has grown enough to become symptomatic) is 2 to 2.4 years for women in their 40s, compared with 4 to 4.1 years for women ages 70 to 74, ACOG estimates. Annual mammograms starting at age 40 provide a better chance of finding and treating breast cancer in an early stage.5,12