The screening mammography debate has been rekindled by the American Cancer Society’s updated guideline released in October 2015. Surgeons are now looking at yet another iteration of the optimal surveillance schedule aimed at reducing breast cancer mortality.
Nearly all breast cancer patients undergo surgery as at least one component of their care through diagnostic biopsy and/or definitive locoregional management, and many women are referred to surgeons for evaluation as well as follow-up for a variety of benign breast problems. The discussion of breast cancer screening with patients can be complicated by the many guidelines with conflicting recommendations, not to mention patient fears triggered by incompletely informed or simplistic media coverage. Surgeons are therefore obliged to remain knowledgeable regarding the status and rationale for breast cancer screening guidelines that have been developed by our colleagues in the American Cancer Society as well as other organizations.
Context of the updated guideline
The American Cancer Society and the American College of Surgeons have historically advocated in favor of annual screening mammography for average-risk women in the United States beginning at age 40 years (https://goo.gl/4W92EI). In 2009, the United States Preventive Services Task Force (USPSTF) published a recommendation that women delay initiation of screening mammography until reaching age 50, with follow-up studies performed biennially thereafter. This USPSTF guideline has remain unchanged as of 2015 (http://goo.gl/RYYWEP). Other medical societies and institutions have established their own guidelines.
The updated American Cancer Society guideline now recommends that average-risk women initiate annual mammography at age 45, but advocates in favor of availability of annual mammography beginning at age 40; the updated guideline also indicates that women can transition to biennial mammography at age 55, but should have access to continued annual mammography in accordance with personal preferences and after consideration of risks and benefits (JAMA. 2015;314:1599-614).
The updated guideline can basically be interpreted as a more relaxed version of the prior guideline, which featured a straightforward mandate for average-risk women to undergo annual screening mammography beginning at age 40 years. However, the increased complexity of the more flexible guideline has generated legitimate concerns regarding the potential for confusion and misinterpretation.
Updated guideline rationale and empirical basis
The Society commissioned a systematic review to evaluate the benefits and harms of mammographic screening as well as clinical breast examination, based upon randomized clinical trials, and observational and modeling studies (JAMA. 2015;314: 1615-34).
The Society then convened their Guideline Development Group (GDG) and GDG Breast Subgroup to interpret the systematic review for the purpose of drafting the breast cancer screening update. This process was further guided by a panel of External Expert Advisors. Mortality reductions were analyzed in the context of population-based breast cancer incidence rates by 5-year age increments.
Not surprisingly, the overall review confirmed the findings of several published studies that screening mammography in women aged 40-79 reduces breast cancer mortality rates by 20%-50%, with extent of benefit varying by age, as well as study design (randomized clinical trial versus observational). Since breast cancer incidence rates increase substantially among women by age (incidence rates per 100,000 population for women 35-39; 40-44; 45-49; 50-54; and 55-59 reported as 59.5; 122.5; 188.6; 224.0; and 266.4, respectively), the likelihood of a mammogram detecting a true cancer clearly increases with age. The American Cancer Society GDG Breast Subgroup balanced the mortality reductions and population-based incidence rates against the risks of mammography “harms” (defined as needing to be recalled for additional testing via imaging and/or biopsy).
The quality of evidence for estimating risk of “overdiagnosis” (detecting a breast cancer that was not destined to be biologically significant or life threatening) was deemed to be insufficient and so this controversial metric was omitted from the final analysis. However, data regarding the general tendency for breast cancers to have more favorable biologic features (and therefore presumed to be more indolent) in older-aged women were taken into account with regard to recommendations for age-based screening intervals.
Upon review of the above incidence and mortality-related issues, the Society generated their age- and interval-based mammography screening recommendations. The recommendations were stratified as either “strong” (defined as a screening practice that “most” patients should follow, and one that could be reasonably used as a “quality criterion or performance indicator”) or “qualified” (defined as a screening practice that is reasonable for the “majority” of patients, but encouraging a balanced discussion of possible alternatives and informed decision making). The recommendations for average-risk women are summarized as follows:
• Strong Recommendation: Women should initiate screening mammography at age 45 years.