Annual mammography starting at age 40: More talk, less action?
SCREENING EVERY YEAR VS EVERY 2 YEARS
Also controversial is whether screening mammography should be done annually or every 2 years. For women in their 50s, the American Cancer Society recommends mammography every year, the American College of Physicians and American Academy of Family Physicians recommend it every 1 to 2 years, and the USPSTF recommends it every 2 years.
A prospective analysis of 11,474 women with breast cancer and 922,624 controls8 found that performing mammography every 2 years instead of annually for women age 50 to 74 did not increase the risk of advanced-stage or large-size tumors regardless of breast density or hormone therapy use. But women undergoing annual mammography had a higher risk of false-positive results and biopsy recommendations.8 Women age 40 to 49 with extremely dense breasts were the only subgroup who derived additional benefit from annual screening, as they had a higher risk of advanced-stage cancer if they were screened every 2 years instead of yearly (odds ratio [OR] 1.89; 95% CI 1.06–3.39) and a higher risk of larger tumors (OR 2.39; 95% CI 1.37–4.18). However, the probability of a false-positive result in these younger women undergoing annual mammography was also very high at 65.5%.8
For most women in their 40s (other than those with extremely dense breasts) and 50s, biennial and annual mammography were associated with a similar risk of advanced-stage disease. Women with fatty breasts are at low risk of breast cancer regardless of other risk factors and did not appear to benefit from annual screening.8 The 12% to 15% of women in their 40s with extremely dense breasts (whose risk of breast cancer is similar to that in average-risk women in their 50s) should decide if the added benefit of annual screening is outweighed by the additional harms, including doubling the number of mammograms, as well as more false-positive results and breast biopsy recommendations.8
Mandelblatt et al9 statistically evaluated 20 screening strategies, ie, screening every year or every 2 years, and starting and stopping at various ages. On average, screening every 2 years was 81% as beneficial as annual screening but caused only about half as many false-positive results. Women age 50 through 69 who were screened every 2 years achieved a median 16.5% (range 15%–23%) reduction in breast cancer deaths compared with no screening. Initiating screening every 2 years at age 40 reduced the death rate by an additional 3% (range 1%–6%) compared with starting at age 50. Not surprisingly, starting screening at age 40 consumed more resources and yielded more false-positive results. After age 69, screening every 2 years yielded some additional mortality reduction in all models, but overdiagnosis increased most substantially at older ages, as the ratio of slow- to fast-growing tumors increases with age. The authors concluded that screening every 2 years achieves most of the benefit of annual screening with less harm.
FALSE-POSITIVE RESULTS AND ANXIETY
False-positive results on mammography can increase distress and anxiety about breast cancer and perceived breast cancer risk in some women.3 After 10 years of annual screening, more than half of women receive at least one false-positive recall, and 7% to 9% receive a false-positive biopsy recommendation. It is helpful for women to understand this risk when deciding whether to start mammographic screening.10
OUR VIEWS
There are two major issues to address in clinical practice regarding mammographic screening: at what age to start, and how often to screen. For years, women have been instructed to start annual mammographic screening at age 40, and such established patterns can be difficult to change.
When deciding whether to have a mammogram at age 40, women should be aware of the full range of risks and benefits. Assessing a woman’s individual risk of breast cancer (based on family history and number and age of pregnancies) can be an important starting point for assessing the potential benefits and risks of screening.
Although a shared decision-making approach is intuitively appealing, it takes much more time than simply ordering a mammogram. Time constraints during a medical appointment may make it challenging to have a prolonged discussion about the pros and cons of screening. Patient education materials about the risks vs benefits of screening initiation may be useful, and because the decision does not usually need to be made urgently, women can be given the opportunity to consider the decision outside of the primary care appointment.
The issue of annual vs biennial screening presents an additional challenge, because women have come to expect annual screening. Studies show that the only subgroup of women who appear to benefit from annual screening are those in their 40s with dense breasts. Although breast cancer is rarer in younger women, when it does develop, it is often more aggressive, so offering annual screening to this subpopulation may make sense. For all other women, since there is no evidence that annual mammography offers clinical benefit over biennial screening, clinicians can be comfortable with offering screening every 2 years.
Future research must focus on developing better tools for differentiating women who are at higher vs lower risk for breast cancer and on developing methods to determine which DCIS cancers are more likely to be indolent and therefore amenable to watchful waiting.
In the interim, we must continue to identify women at high risk who will benefit from magnetic resonance imaging, genetic testing, and prophylactic medications, in accordance with USPSTF recommendations. Women with new breast symptoms or concerns should continue to undergo evaluation with diagnostic imaging, including mammography. However, for most women who are at average risk and have no symptoms, we must ensure that they are fully aware of the possible benefits and risks of screening mammography so that they can make an informed decision about when to start screening and how often to be screened.
