Breast Cancer Screening Guidelines
Breast cancer screening guidelines for average-risk women, from the American Cancer Society (ACS) and the United States Preventive Services Task Force (USPSTF), are commonly cited by primary care physicians as very influential in guiding their recommendations to patients. Both organizations endorse the importance of mammography screening, but they differ in their recommendations for the age to begin and end screening, and in the screening interval (Table 3).
In 2002, the USPSTF had recommended mammography for women aged 40 years and older, with or without CBE, every 1 to 2 years. This recommendation was similar to the ACS guidelines, which recommend annual mammography and CBE for women beginning at 40 years of age. Also, similar to the ACS, the USPSTF had stated that the evidence that mammography screening was beneficial in women aged 40 to 69 was generalizable to women 70 years of age and older “if their life expectancy is not compromised by comorbid disease”—and essentially concluding that as long as a woman was in good health, mammography screening could be expected to be beneficial. The ACS recommendation for annual screening was based on improved sensitivity of mammography with annual vs biennial screening, especially in women under age 50, whereas the USPSTF recommendation for screening every 1 to 2 years was based on RCT evidence showing a mortality reduction associated with annual and biennial testing, and the absence of an RCT comparing the two intervals. In 2009, the USPSTF modified its recommendations, withdrawing a recommendation that women aged 40 to 49 undergo routine mammography screening every 1 to 2 years in favor of individualized decisions, and changing the recommendation that women 50 to 74 years of age be screened with mammography every 1 to 2 years to a biennial screening interval. In the updated recommendations, the USPSTF also concluded that there was insufficient evidence to assess the balance of benefits and harms of CBE, and also mammography screening for women 75 years of age and older.
Although evidence from age-specific meta-analyses of RCT data showed similar mortality reductions from women randomized in their 40s and 50s, the USPSTF concluded that since a woman’s absolute risk of breast cancer during her 40s was lower, and the harms of screening were judged to be similar or slightly higher compared with older women, there was “moderate certainty that the net benefit was small.” The underpinnings of this decision can be challenged on several points; First, the USPSTF chose to rely only on meta-analysis of RCT data, which as described above results in an underestimate of the benefit of modern mammography. This is especially problematic because the first generation of RCTs screened women under age 50 with protocols (2-year interval, single-view mammography, etc) that were shown to be ineffective in younger women. Second, while the absolute risk to women in their 40s is less than that of women in their 50s and 60s, it is not trivial; death from breast cancer is the leading cause of cancer-related premature mortality in women, and a leading cause of premature death from all causes. Third, the USPSTF overestimated the impact of the harms relative to benefits in two ways: 1) screening benefits estimated by the RCTs were compared with harms based on modern rates of false-positive results from a mammography surveillance registry. Since the true benefit of screening is underestimated in the RCTs because some women in the invited group are not exposed to any or all screening rounds, comparing harms measured among all women attending community based screening overestimates harms relative to benefits; 2) evidence that showed women are aware of false-positive results and regard them as an acceptable tradeoff for the benefits of early detection was not included in the systematic review.
There is strong evidence that mammography screening is an effective strategy to reduce the incidence of advanced breast cancer. Therefore, it is a means to reduce mortality by creating the opportunity to initiate breast cancer treatment earlier in the natural history of the disease. For screening programs to be successful, high rates of adherence to regular attendance must be coupled with high-quality screening and prompt delivery of state-of-the-art treatment for women diagnosed with breast cancer. Because screening is inherently imperfect, efforts must be equally focused on reducing the adverse effects of false-positive tests, especially the fraction that is avoidable. Organized screening programs tend to be more successful in delivering high-quality screening and thus are preferable to opportunistic screening.
Financial Disclosure: The authors have no significant financial interest or other relationship with the manufacturers of any products or providers of any service mentioned in this article.